[Qt] Enable support for Qt's HighDpiScaling
[Qt] Enable support for Qt's HighDpiScaling

This was missed in the bump to Qt 5.6 and should resolve issues
with window/text scaling on High DPI devices.

ColossusCoinXT/ColossusCoinXT,PIVX-Project/PIVX,presstab/PIVX,benzmuircroft/REWIRE.io,Mrs-X/Darknet,npccoin/npccoin,benzmuircroft/REWIRE.io,Darknet-Crypto/Darknet,npccoin/npccoin,PIVX-Project/PIVX,PIVX-Project/PIVX,48thct2jtnf/P,Bloom-Project/Bloom,48thct2jtnf/P,benzmuircroft/REWIRE.io,Bloom-Project/Bloom,48thct2jtnf/P,ColossusCoinXT/ColossusCoinXT,PIVX-Project/PIVX,Mrs-X/Darknet,npccoin/npccoin,PIVX-Project/PIVX,ColossusCoinXT/ColossusCoinXT,ColossusCoinXT/ColossusCoinXT,PIVX-Project/PIVX,presstab/PIVX,npccoin/npccoin,benzmuircroft/REWIRE.io,48thct2jtnf/P,Mrs-X/Darknet,Bloom-Project/Bloom,Bloom-Project/Bloom,PIVX-Project/PIVX,npccoin/npccoin,presstab/PIVX,Darknet-Crypto/Darknet,Mrs-X/PIVX,48thct2jtnf/P,benzmuircroft/REWIRE.io,Mrs-X/PIVX,Mrs-X/Darknet,ColossusCoinXT/ColossusCoinXT,Bloom-Project/Bloom,presstab/PIVX,48thct2jtnf/P,Mrs-X/PIVX,PIVX-Project/PIVX,presstab/PIVX,Darknet-Crypto/Darknet,ColossusCoinXT/ColossusCoinXT,Mrs-X/Darknet,npccoin/npccoin,Mrs-X/PIVX,Mrs-X/PIVX,Mrs-X/PIVX,PIVX-Project/PIVX,benzmuircroft/REWIRE.io,Mrs-X/Darknet,presstab/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,Bloom-Project/Bloom,Darknet-Crypto/Darknet