Replaced MapViewAnimator implementation.

Now supports cubic bezier timing functions. Animation progress is now calculated based on time instead of steps to make them smooth and unaffected by unrelated performance hickups.

A CubicBezier object can be created by specifying two handle points.
Several web-applications exist to generate these points. E.g. http://cubic-bezier.com/
Added CubicBezier.cs to project.
Merge pull request #152 from txsmith/master

Improvements to MapViewAnimator