Added support for non-VR and in-game menu.

For this update, I've added support for all the fine folks here on Itch who do not have a VR headset and are interested in experiencing Over Then Under. If you launch the game's .exe file without a VR headset connected, the VR player character will spawn a keyboard and mouse player and destroy itself. Next time, I'll have the game-mode evaluate which player to spawn and then spawn it that way.

I also felt bad that PC players have to alt+f4 to close the game, so I finally fixed the in-game menu for both VR and PC players. If you tap "E" on the keyboard, you will open the menu. Alternatively, if you're a VR player, press either "Y" on your Quest controller or "B" on your Index knuckles.