Slight bug fixes, minor additions!

Hey!

Made some minor changes today and yesterday while I was in hospital. These should hopefully fix a number of bugs, which (off the top of my head) are:

• The screen going black randomly after quitting a level or dying - Fixed by editing a Post Draw event line of code.
• Randomly getting the game over sequence at the beginning of a level, or having the music slowdown effect in the menu - Added a failsafe "GAMEMODES.DEFAULT" mode. The Main Controller CANNOT trigger gameover code while this mode is set.

Of a more major note, I've added an announcer! This will announce certain things in the game in an old 80s retro style of voice. It can be disabled, of course.

Have fun!