Refactor MOAIEaseType

[Vavius]

Currently, MOAIEaseType is used in two different fashions:

1. As a true ease type in MOAIEaseDriver and MOAINode's animation helpers - seekAttr, moveAttr, seekLoc, etc (I suppose those are the most used animation routines in MOAI)
2. As an animcurve key interpolation mode

What I'm suggesting is to split it to two different classes: one for ease drivers, second is for key interpolation:

1. Ease driver can have more ease types: circ, sine, bounce, back, elastic (those are widely used in js, as3 and other frameworks). Some of them can have parameters, like frequency for elastic, overshoot for back.
2. Curve key interpolation can have only 3 types: flat, linear, bezier. The last one gives you the control points for left and right tangents. This works best in visual curve editor. So we can keep existing interpolation types, as they are easier to create from code.