New Main Menu with 3D Backgrounds and Selectable Buttons

[cdsupina]

• Currently failing test_minimal_headless_audioless_game_gets_to_main_menu appears to be issues loading assets
• Menu button art by @DH
• Sound effects for button interactions
• Randomized 3D background
• Animated logo

[varoonp123]

My only reservation to merging this is the thetawave_logo_spritesheet.png asset. It is our single largest free asset. Larger than the 3d models...........

I know 14Mb isnt a lot when the file is already on your computer, but this file needs to be sent over the internet every time the game loads in the browser. Plus the 7Mb logo used at landing page. That's another 1-5 seconds of a black screen between clicking "Start Game" and getting thetawave to start loading on standard 4G internet speeds.