Bug fixes and code improvements.
-FEATURE: FireFlies will now change their "distance deviation" over
time.
-FEATURE: Extra life-bonuses will not be picked up if the Player has
maximum lives.
-FEATURE: Changed colour of Invulnerability bonuses.
-OTHER: Updated .gitignore with "/libs".
-OTHER: Updated .classpath due to earlier update of LibGDX files.
-CODE: Added a colour parameter to Enemy's constructor.
-CODE: Changed Enemy's getColour() to return a variable (color_) instead
of being abstract.
-CODE: Removed all methods overriding Enemy's getColour().
-CODE: Fixed errors that followed the LibGDX update.
-BUG: FireFlies always added pi/2 when moving to orbit, disregarding its
orbit direction.
-BUG: Snakes and BabySnakes would only spawn downwards.