Added events for KeyUp and KeyDown

The KeyUp and KeyDown methods are very important for low level keyboard
access but in MonoGame the general solution of overriding the view
cannot be done so I expose both as events.
Revert "Added events for KeyUp and KeyDown"

This reverts commit c4f6d7a84a181ce1c8616913f9126639fd15839e.
[MacOS] Added an optional Delegate to GameWindow

Added an optional Delegate to GameWindow to allow custom GameWindow
implementations to be used.
[MacOS] Changed Delegate to CreateWindowDelegate
Merge pull request #1256 from SamuelEnglard/develop3d

[MacOS] Added an optional Delegate to GameWindow