MathUtil: Make Rectangle work with unsigned types.
Revert "Citra GLFW: Clean up some functions."

This reverts commit 77e2b666fc5ae0ec5c2f0905838510c44053250d.
I'm done bothering with this stuff.
EmuWindow: Add a TODO.

Implementing this function currently is not critical, as we don't perform any configuration changes, yet.

However, the interface is a good starting point for adding this functionality.
citra-qt: Small cleanup.
EmuWindow: Add some explicit documentation and set proper minimal client area size.
citra GLFW: Ignore minimal window size hints.

GLFW provides no proper support for this, hence we just allow any window size to be used.
citra-qt: Fix a potential crash.