Re-phrased some odd wording.
grabcut.py sample: Allow drawing rect from bottom/right

The grabcut sample script isn't able to create rectangles correctly that are
drawn from e.g. bottom-right to top-left.
This small commit uses four min() calls to determine the correct
top-left point of the rectangle.
It also removes some unnecessary white spaces before colons.
fixed spelling and removed return images
Merge pull request #1851 from dneelyep:patch-1
Merge pull request #2313 from m3d:patch-1
Merge pull request #2311 from SvenWe:master