Theming and keystore fix.

Fixed the location of keystore on Windows and OSX, and changed the theming to be more suitable for ATH.
Linux binaries are only suitable for ubuntu 16.04 or newer. Other distributions might work too.

Sha256 sums:

ATHDesktopWallet_Windows_64bit.zip:
22f2d682a6151349dd88e480c1c5b1270aaefdc478c58ad235fa261c46c4e606

ATHDesktopWallet_Windows_32bit.zip:
80ecbffd7b0060c99a10205c264f8835ffd2de78da96a2caae70efadfe77c925

ATHDesktopWallet_Linux_64bit.zip:
bf1cd0ce09ba3866b07eeecd9847c43bf5044304e9792f9381fba360c0e57eb7

ATHDesktopWallet_OSX_64bit.dmg:
aed8095800f8e76ad307e3c77ad2a070c4eec7cf3350dcd1b526b1d2877ffa2c