Virtual Keyboard: Implement DPI Scaling

* Use layoutScale and pixmapScale from IMEDataInterface to:
    Scale IME Pixmaps on load
    Scale Tablet Keyboard layout
    Scale Tablet Keyboard font sizes
* Scale to a percent of the screen size instead of arbitrary values

Open-WebOS-DCO-1.0-Signed-Off-By: Josh Palmer <jpalmerwatkins@me.com>