gui: Handle WalletModel::unload asynchronous
gui: Handle WalletModel::unload asynchronous

This change prevents deleting a WalletModel instance while it's
being used.

Sjors/bitcoin,n1bor/bitcoin,rnicoll/bitcoin,midnightmagic/bitcoin,kallewoof/bitcoin,kallewoof/bitcoin,namecoin/namecore,vertcoin/vertcoin,vertcoin/vertcoin,prusnak/bitcoin,ElementsProject/elements,tecnovert/particl-core,anditto/bitcoin,namecoin/namecoin-core,MeshCollider/bitcoin,kallewoof/bitcoin,jamesob/bitcoin,MarcoFalke/bitcoin,pstratem/bitcoin,jnewbery/bitcoin,pataquets/namecoin-core,GroestlCoin/GroestlCoin,pstratem/bitcoin,Sjors/bitcoin,jamesob/bitcoin,domob1812/namecore,qtumproject/qtum,cdecker/bitcoin,domob1812/bitcoin,fanquake/bitcoin,yenliangl/bitcoin,EthanHeilman/bitcoin,andreaskern/bitcoin,bitcoinsSG/bitcoin,pstratem/bitcoin,midnightmagic/bitcoin,GroestlCoin/bitcoin,jamesob/bitcoin,qtumproject/qtum,prusnak/bitcoin,dscotese/bitcoin,andreaskern/bitcoin,MeshCollider/bitcoin,GroestlCoin/bitcoin,JeremyRubin/bitcoin,dscotese/bitcoin,MeshCollider/bitcoin,Xekyo/bitcoin,fanquake/bitcoin,ElementsProject/elements,peercoin/peercoin,domob1812/bitcoin,alecalve/bitcoin,mm-s/bitcoin,instagibbs/bitcoin,GroestlCoin/GroestlCoin,domob1812/namecore,rnicoll/bitcoin,GroestlCoin/GroestlCoin,ElementsProject/elements,qtumproject/qtum,alecalve/bitcoin,tecnovert/particl-core,andreaskern/bitcoin,pataquets/namecoin-core,mm-s/bitcoin,particl/particl-core,sipsorcery/bitcoin,namecoin/namecore,rnicoll/bitcoin,yenliangl/bitcoin,jambolo/bitcoin,Sjors/bitcoin,ajtowns/bitcoin,jamesob/bitcoin,rnicoll/dogecoin,ElementsProject/elements,DigitalPandacoin/pandacoin,jonasschnelli/bitcoin,rnicoll/bitcoin,midnightmagic/bitcoin,sipsorcery/bitcoin,peercoin/peercoin,MeshCollider/bitcoin,vertcoin/vertcoin,fujicoin/fujicoin,sstone/bitcoin,MeshCollider/bitcoin,fanquake/bitcoin,lateminer/bitcoin,mruddy/bitcoin,bitcoinknots/bitcoin,DigitalPandacoin/pandacoin,jamesob/bitcoin,mm-s/bitcoin,monacoinproject/monacoin,tecnovert/particl-core,instagibbs/bitcoin,bitcoin/bitcoin,andreaskern/bitcoin,mruddy/bitcoin,tecnovert/particl-core,JeremyRubin/bitcoin,GroestlCoin/bitcoin,ahmedbodi/vertcoin,apoelstra/bitcoin,anditto/bitcoin,namecoin/namecore,MarcoFalke/bitcoin,litecoin-project/litecoin,fanquake/bitcoin,fujicoin/fujicoin,AkioNak/bitcoin,bitcoinsSG/bitcoin,AkioNak/bitcoin,andreaskern/bitcoin,jambolo/bitcoin,kallewoof/bitcoin,litecoin-project/litecoin,mm-s/bitcoin,midnightmagic/bitcoin,DigitalPandacoin/pandacoin,domob1812/namecore,jnewbery/bitcoin,DigitalPandacoin/pandacoin,AkioNak/bitcoin,AkioNak/bitcoin,cdecker/bitcoin,yenliangl/bitcoin,achow101/bitcoin,kallewoof/bitcoin,domob1812/bitcoin,jlopp/statoshi,namecoin/namecoin-core,lateminer/bitcoin,litecoin-project/litecoin,n1bor/bitcoin,particl/particl-core,yenliangl/bitcoin,pataquets/namecoin-core,achow101/bitcoin,achow101/bitcoin,practicalswift/bitcoin,bitcoinsSG/bitcoin,EthanHeilman/bitcoin,fujicoin/fujicoin,bitcoin/bitcoin,yenliangl/bitcoin,jonasschnelli/bitcoin,EthanHeilman/bitcoin,vertcoin/vertcoin,fujicoin/fujicoin,apoelstra/bitcoin,cdecker/bitcoin,rnicoll/dogecoin,rnicoll/dogecoin,practicalswift/bitcoin,lateminer/bitcoin,Xekyo/bitcoin,pataquets/namecoin-core,alecalve/bitcoin,instagibbs/bitcoin,ajtowns/bitcoin,mm-s/bitcoin,practicalswift/bitcoin,namecoin/namecoin-core,yenliangl/bitcoin,achow101/bitcoin,jlopp/statoshi,domob1812/bitcoin,tecnovert/particl-core,rnicoll/bitcoin,namecoin/namecoin-core,jonasschnelli/bitcoin,cdecker/bitcoin,qtumproject/qtum,anditto/bitcoin,DigitalPandacoin/pandacoin,bitcoinknots/bitcoin,cdecker/bitcoin,sipsorcery/bitcoin,lateminer/bitcoin,apoelstra/bitcoin,dscotese/bitcoin,pataquets/namecoin-core,bitcoinknots/bitcoin,dscotese/bitcoin,jambolo/bitcoin,MeshCollider/bitcoin,Xekyo/bitcoin,achow101/bitcoin,litecoin-project/litecoin,jlopp/statoshi,EthanHeilman/bitcoin,anditto/bitcoin,sstone/bitcoin,domob1812/namecore,litecoin-project/litecoin,EthanHeilman/bitcoin,GroestlCoin/bitcoin,ahmedbodi/vertcoin,sstone/bitcoin,AkioNak/bitcoin,bitcoin/bitcoin,domob1812/namecore,namecoin/namecoin-core,sipsorcery/bitcoin,namecoin/namecore,ahmedbodi/vertcoin,bitcoin/bitcoin,jlopp/statoshi,sstone/bitcoin,alecalve/bitcoin,MarcoFalke/bitcoin,jnewbery/bitcoin,bitcoinsSG/bitcoin,achow101/bitcoin,mruddy/bitcoin,jambolo/bitcoin,cdecker/bitcoin,ahmedbodi/vertcoin,bitcoinsSG/bitcoin,ElementsProject/elements,mruddy/bitcoin,n1bor/bitcoin,jnewbery/bitcoin,jonasschnelli/bitcoin,jnewbery/bitcoin,DigitalPandacoin/pandacoin,MarcoFalke/bitcoin,lateminer/bitcoin,jlopp/statoshi,namecoin/namecore,sipsorcery/bitcoin,JeremyRubin/bitcoin,rnicoll/bitcoin,mruddy/bitcoin,Xekyo/bitcoin,jonasschnelli/bitcoin,midnightmagic/bitcoin,domob1812/bitcoin,monacoinproject/monacoin,dscotese/bitcoin,bitcoin/bitcoin,MarcoFalke/bitcoin,monacoinproject/monacoin,pstratem/bitcoin,domob1812/bitcoin,particl/particl-core,practicalswift/bitcoin,Sjors/bitcoin,peercoin/peercoin,ajtowns/bitcoin,n1bor/bitcoin,GroestlCoin/GroestlCoin,apoelstra/bitcoin,anditto/bitcoin,peercoin/peercoin,lateminer/bitcoin,sipsorcery/bitcoin,Xekyo/bitcoin,GroestlCoin/GroestlCoin,fanquake/bitcoin,midnightmagic/bitcoin,vertcoin/vertcoin,dscotese/bitcoin,monacoinproject/monacoin,qtumproject/qtum,qtumproject/qtum,anditto/bitcoin,ajtowns/bitcoin,GroestlCoin/bitcoin,pstratem/bitcoin,particl/particl-core,ElementsProject/elements,domob1812/namecore,mruddy/bitcoin,Xekyo/bitcoin,MarcoFalke/bitcoin,prusnak/bitcoin,GroestlCoin/bitcoin,sstone/bitcoin,particl/particl-core,n1bor/bitcoin,JeremyRubin/bitcoin,peercoin/peercoin,Sjors/bitcoin,namecoin/namecore,monacoinproject/monacoin,JeremyRubin/bitcoin,vertcoin/vertcoin,bitcoinsSG/bitcoin,JeremyRubin/bitcoin,jambolo/bitcoin,peercoin/peercoin,namecoin/namecoin-core,alecalve/bitcoin,jamesob/bitcoin,tecnovert/particl-core,bitcoin/bitcoin,practicalswift/bitcoin,rnicoll/dogecoin,pstratem/bitcoin,litecoin-project/litecoin,instagibbs/bitcoin,jambolo/bitcoin,instagibbs/bitcoin,ajtowns/bitcoin,ajtowns/bitcoin,n1bor/bitcoin,AkioNak/bitcoin,instagibbs/bitcoin,ahmedbodi/vertcoin,jlopp/statoshi,sstone/bitcoin,kallewoof/bitcoin,practicalswift/bitcoin,apoelstra/bitcoin,GroestlCoin/GroestlCoin,prusnak/bitcoin,qtumproject/qtum,prusnak/bitcoin,rnicoll/dogecoin,mm-s/bitcoin,fujicoin/fujicoin,apoelstra/bitcoin,prusnak/bitcoin,pataquets/namecoin-core,alecalve/bitcoin,monacoinproject/monacoin,andreaskern/bitcoin,ahmedbodi/vertcoin,EthanHeilman/bitcoin,fanquake/bitcoin,fujicoin/fujicoin,bitcoinknots/bitcoin,bitcoinknots/bitcoin,particl/particl-core