Make Navigation Bar and Pie COntrols share the same button layout

Based on the commit series for pie controls, this commit
makes the Navigation Bar and Pie Controls share
the same button layout. However, there is no button layout
editor for pie controls, which makes the navigation bar
the leading entity when it comes to button layouts.

This commit introduces:
* A common notion of navigation buttons used in CyanogenMod.
  (class NavigationButtons)
* Some setting constants changes to avoid clashes with PA.
* Removal of the pie search key, since it is no longer needed.
* Sophisticated key event injection.
* Virtual key sound effect