notify about pending long press

Recovery changes:

- add a method to the UI class that is called when a key is held down
  long enough to be a "long press" (but before it is released).
  Device-specific subclasses can override this to indicate a long
  press.

- do color selection for ScreenRecoveryUI's menu-and-log drawing
  function.  Subclasses can override this to customize the colors they
  use for various elements.

- Include the value of ro.build.display.id in the menu headers, so you
  can see on the screen what version of recovery you are running.

Change-Id: I426a6daf892b9011638e2035aebfa2831d4f596d