add ok button for currencies
add ok button for currencies

also update the currency list when changing exchanges.  defaults to
first in list if current selected currency is not available on the other
exchange

spesmilo/electrum,dabura667/electrum,dabura667/electrum,romanz/electrum,cryptapus/electrum,vertcoin/electrum-vtc,aasiutin/electrum,lbryio/lbryum,spesmilo/electrum,dashpay/electrum-dash,vialectrum/vialectrum,wakiyamap/electrum-mona,cryptapus/electrum-myr,neocogent/electrum,vertcoin/electrum-vtc,vertcoin/electrum-vtc,fyookball/electrum,argentumproject/electrum-arg,dashpay/electrum-dash,lbryio/lbryum,FairCoinTeam/electrum-fair,romanz/electrum,fyookball/electrum,asfin/electrum,fireduck64/electrum,kyuupichan/electrum,spesmilo/electrum,FairCoinTeam/electrum-fair,pooler/electrum-ltc,vertcoin/electrum-vtc,neocogent/electrum,cryptapus/electrum-myr,vialectrum/vialectrum,digitalbitbox/electrum,digitalbitbox/electrum,pooler/electrum-ltc,aasiutin/electrum,fireduck64/electrum,fujicoin/electrum-fjc,fireduck64/electrum,cryptapus/electrum-uno,imrehg/electrum,dashpay/electrum-dash,fyookball/electrum,asfin/electrum,cryptapus/electrum,romanz/electrum,cryptapus/electrum-uno,cryptapus/electrum-uno,neocogent/electrum,protonn/Electrum-Cash,digitalbitbox/electrum,pooler/electrum-ltc,molecular/electrum,molecular/electrum,spesmilo/electrum,argentumproject/electrum-arg,fujicoin/electrum-fjc,cryptapus/electrum-myr,cryptapus/electrum,kyuupichan/electrum,vialectrum/vialectrum,dabura667/electrum,aasiutin/electrum,kyuupichan/electrum,imrehg/electrum,pknight007/electrum-vtc,procrasti/electrum,molecular/electrum,imrehg/electrum,pknight007/electrum-vtc,FairCoinTeam/electrum-fair,imrehg/electrum,asfin/electrum,pknight007/electrum-vtc,fujicoin/electrum-fjc,argentumproject/electrum-arg,cryptapus/electrum-uno,wakiyamap/electrum-mona,wakiyamap/electrum-mona,procrasti/electrum,dashpay/electrum-dash,digitalbitbox/electrum,wakiyamap/electrum-mona,protonn/Electrum-Cash,protonn/Electrum-Cash,pooler/electrum-ltc,protonn/Electrum-Cash,molecular/electrum,argentumproject/electrum-arg,cryptapus/electrum-myr,aasiutin/electrum,dabura667/electrum,procrasti/electrum,fireduck64/electrum,procrasti/electrum,pknight007/electrum-vtc,FairCoinTeam/electrum-fair