ANG-528: SimpleIntegerPicker arrow buttons now follow design spec

* Converted SimpleIntegerPicker to use font-based icons.
* SimpleIntegerPicker now applies a "pressed" class to the buttons for that state.
* Height of SimpleIntegerPicker is now able to be easily adjusted.
* RTL arrows are flipped horizontally instead of rotated.
* Switched the icon font characters to LESS variables so it's easier for other widgets to use use them.

Enyo-DCO-1.1-Signed-off-by: Blake Stephens <blake.stephens@lge.com>