Updated Documentation (HoughCircles)

Rewrite the note on HoughCircles documentation to make it more clear

Add note to clarify that the output vector of found circles is sorted by
descending order of centres accumulator values.

Also delete reductant lines on the HoughCircles documentation.

Added comments to hough circles function.

Added comments to icvhoughgradient

Misalignment in line 1183 corrected
Merge pull request #3443 from HelenWong:bug3363Fix