Restyling

Did an expansive rewrite of the theming capabilities of QGC. The primary work was:
 * Moving as much theming to the stylesheets as possible
 * Synchronizing the light & dark themes
 * Adding theme support to the custom drawing widgets (HUD, HSI, etc.)
 * Removing the native theme option
 * Reworking the themes with a goal towards higher contrast and consistent coloring/design.

Dark theme:
![screenshot from 2013-06-02 10 14 44](https://f.cloud.github.com/assets/206363/596593/72e3fb5a-cba8-11e2-9141-d2d25d012615.png)

Light theme:
![screenshot from 2013-06-02 10 14 50](https://f.cloud.github.com/assets/206363/596594/7c9d17ee-cba8-11e2-8455-74ebc6fe0780.png)