Overhaul the Win32 UI with simplification and organisation.

 New things include:
-File -> Savestate Slot: Lets the user pick the savestate slot to be used.
-Game Settings -> More Settings...: Opens the main settings screen from anywhere.
-Game Settings -> Control Mapping...: Opens the key mapping screen from anywhere.
-Infrequently changed options were removed. They can still be accessed via More Settings or going to the main settings menu.
-Organised menus; nothing is out of place anymore.
-Simplified menus: as some options were removed or moved, it's easier to find what you're looking for, now.
-Fix a few warnings in WndMainWindow.cpp.

File:
![File Menu](https://i.minus.com/ieaPt9QYtK8CO.PNG)

Emulation:
![Emu Menu](https://i.minus.com/ixkV2UiLzgPLh.PNG)

Debug:
![Debug Menu](https://i.minus.com/iuSwh35cXjGoV.PNG)

Game Settings:
![Settings Menu](https://i.minus.com/i0lcBJDutzuNV.PNG)

So as you can see, it's still familiar, yet vastly simplified and organised.

Prior discussion: https://github.com/hrydgard/ppsspp/issues/3624