Fixes #14846.  Add arrow keyboard support to mobile/Slider and fix flipped vertical Slider to increase in value from top to bottom.
Fixes #14846.  Add arrow keyboard support to mobile/Slider and fix flipped vertical Slider to increase in value from top to bottom.

git-svn-id: ee6e786acc44c9cca5ee17c71a5576c45c210361@27948 560b804f-0ae3-0310-86f3-f6aa0a117693

redaktor/deliteful