Add support for Keys.RightControl/Keys.RightShift

This is a new implementation that depends on information found at the
event status.
It doesn;t need CoreWindow.GetKeyState(...) as my previous commit.

We detect RightControl by checking KeyStatus.IsExtendedKey.
To detect RightShift we need to check the scancode.
Merge pull request #1416 from nkast/nkastBranch

Add support for Keys.RightControl/Keys.RightShift
Moved argument checking before platform code.
Added more correct exception for iOS.
Update README.md

Updated build server badge.
Merge pull request #1423 from SickheadGames/GetDataWarn

Texture2D.GetData() Improvements