Perform some Windows UI cleanups. Dozens of unused IDs were leftover from Dolphin, and I doubt they'll ever be used again. Also remove several magic numbers, instead using enumerators to clarify code.
Improve skip frame onscreen messages by removing switch, fix some typos, remove qualifier(generates a non-standard warning for some reason).
Remove more magic numbers and remove enumerator names.
Remove BufferedRendering enumerator name.
Put TextureFiltering enumerator name back. It was deleted by accident.
Correct the 4XXXX menu IDs.
Add license info to WndMainWindow.cpp.
More cleanups.
Merge pull request #2977 from thedax/win32UICleanup

Win32 UI: Major code cleanups.