New: Added support for scaling in CPView

This PR adds the support of scaling in CPView.
There are two new public methods in CPView : -(void)scaleUnitSquareToSize: and -(void)setScaleSize:
-(void)scaleUnitSquareToSize: works exactly as in COCOA, it means if you set a first scale to 0.5 and then 0.5 again, the scaleSize of the view will be 0.25
-(void)setScaleSize: works with the value given. If you set 0.5 after you just seted 0.5 the scaleSize will be 0.5. This method is definitly better in using, specially when using the scaleSize binding with a slider.

Test app in Tests/Manual/ScalingTest
Merge pull request #1998 from Dogild/scaling-support

New: Added support for scaling in CPView