[touch] allow swipe gestures with a perpedicular movement of up to 20 degrees

This allows gestures to be recognised as vertical/horizontal swipes even if
the swipe movement is a bit diagonal (up to 20 degrees from the horizontal
or vertical movement) which improves swipe gesture recognition a lot
especially because most swipe gestures tend to move up/down a bit at the end
of the gesture.
Merge pull request #2512 from Montellese/droid_swipe_variance

[touch] allow swipe gestures with a perpendicular movement of up to 20 degrees