Refactoring

Big refactoring using UIColor native methods - improved performances by drawing gradient only once and changing opacity afterward.
this version uses Quartz to draw everything but is still slow
not working
improvments
Added buttons for testing and fixed setSelectionColor. Also adjusted frame size to match.
limits the position of the selection knob within the active area shape (i.e within the gradient)
added the same limitation for the square shape
added a switch to change picker shape
Merge branch 'Baldoph-performance' of https://github.com/RSully/RSColorPicker into performance
Merge pull request #17 from Baldoph/performance

Improvements - fixes setSelectionColor issues, increases performance, updates demo app, etc.