Settings: improvements to dynamic fee slider
Settings: improvements to dynamic fee slider

Fixes #1595

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