A few small updates made

Updated some of the aesthetics in Mouse Time:

• Made the upper UI bar more lively and distinct.
• Added sound effects to the game (and added a button to let players turn the sound effects off if desired).

Choosing appropriate sound effects turned out to be somewhat awkward. I'm not quite satisfied with the currently implemented sound effects, but they'll do for now. I also haven't been able to find any music that I'd like to use for Mouse Time, but that's a next time thing too.