Fix NavButton AlphaGlow when pressed

Note that since users can set the Navbar Alpha, this will be a relative
brightness. In AOSP the button brightens to 1f alpha when pressed (.7f is not pressed).
if user sets alpha to 1.0, then there will be no difference.

Change-Id: I3d2d863bd4ff0cc2be14718afe3a17d795b77729
Signed-off-by: Zaphod <mwilson@acesappraisal.com>