Huge commit of new feature implementations

-Added 2D particle effect to Note pick-up
-Converted x-position calculate from Python script to C# Unity in-game
code
-Added Main Menu with options to chose levels
-Added Pause functionality
-Added crude "Back" buttons to menus

++Began implementation of 2nd gameplay mode:
-Implemented file browser system
-Added a basic mp3 selection screen
-Looking into cross-platform mp3 solution, still in-progress