Draft: Contrast Focus

Experimental work - added some contrast type focus measures:

FOCUS_STAR_STDDEV - idea from Hy. Seems to work on star based images.

FOCUS_STAR_SOBEL - Sobel style edge detection

FOCUS_STAR_LAPLASSIAN - Laplassian style edge detection

FOCUS_STAR_CANNY - Canny algo

These are alternative focus measures. Need to test them as they may not work well. They could be useful for lunar, solar and planetary focusing - TBC

This makes use of OpenCV which is not currently installed in KStars. If adding this library is problematic the algos could be hand coded in cpp of course.

Added Gaussian curve fitting.

Added ROI box (as per single star sub framing) and ring mask as alternatives to using the full frame. Would be useful for focusing on a lunar crater, sunspot or planetary edge for example.