CCEffectColorChannelOffset - Add CGPoint versions of the offset properties

I should have used CGPoint all along instead of GLKVector2. Since this has been released I
can't change the existing interface so for now I'll add these new ones and deprecate the
GLKVector2 versions. This will all be updated in v4 to use only CGPoint for the offset values.
Merge remote-tracking branch 'origin/develop' into develop