Reviewed VS2015 UWP project

Mouse input is implemented, with all bells-and-whistles. This includes
cursor locking and scroll wheel support.

Keyboard input is reverted to a callback model to better reflect the
existing architecture in "core.c"

Add a basic UWP gampead poll function with zero changes to code outside of App.cpp

Support Universal Windows Platform (UWP):
- Windows 10 App
- Windows Phone
- Xbox One