Migrated NSZombieApocolypse to unified API

- Cast double (Math.Abs with nfloat) to float
- Cast int to nint in order to cast to enum
- Cast nfloat to float
- Changed RectangleF.Empty CGRect.Empty
- Enclosed negative value and parentheses in order to cast to nfloat
Removed incorrect Action casts from UIView.Animate(double, double,
UIViewanimationOptions, Action, Action)
- Removed incorrect CGRect cast