New Tween.start() method

Tween's constructor no longer starts the tween automatically, the user
has to call .start() to get it going. Constructors with side effects
aren't really a good thing!
Eliminate last Fader

BGM manager was still using Fader for volume adjustment, excising it
required major refactoring on the BGM class; BGM manager uses dollarsign
notation; Fader.js removed from project
Update kh2Bar to dollarsign notation

Also converted the reading property to get/set methods, as the
getter/setter syntax is non-standard.
Display move name on acting battler's side

This way it's easier to tell at a glance which side is attacking.