the magnifying glass rim and glass are drawn once as a single image and put overlay to the grid
Loupe: circle path used for masking is created only once
Loupe: the selection square is now part of the static image
last improvements I could think of in drawRect methods….
Merge branch 'refs/heads/master' into loupe_performance

Conflicts:
	RSColorPicker/ColorPickerClasses/BGRSLoupeLayer.m
Merge pull request #22 from Baldoph/loupe_performance

Loupe performance