Fixed mouse behavior

- System cursor no longer appears in-game.
- Mouse can be used in menus, no longer selecting only the option closer
to the center of the screen (i.e. "load game" in main menu).

DualShock3 buttons (X,O) for menu selection

"Main menu" button works when gamestate==GS_FINALE

Meaning, you can pull the main menu with a gamepad
after finishing an episode of the game.

SDL joystick events now work while in menus.

Menu controls changed to take advantage of this.
Also, joystick/gamepad is now enabled by default, and
"main menu" can be bind to a button/key in control options.

ZDoom v2.8.1

- we are past 2.8 now so the version numbers should reflect that.

This is the branch that will not be 2.8.x when it's released

It's not 2.8pre anymore! OMG!

- updated DUMB to 85fa2b7e833e2ec45af7ed9629c9f360e4f37730

* Removed unnecessary code

Version 2.7.1