Implement all easing types in Tween class

Easing functions copied from the unofficial jQuery Easing Plugin
project.
Update MenuStrip to use Tween

Also, fixed a bug in Tween.isFinished() where the meaning of the return
value was reversed
Define UI animation parameters separately

UI classes will have the animation parameters for various transitions
defined near the beginning of the file. This makes it easier to tweak
the animations later.