Navbar buttons spacing for Phablet UI

This patch trys to make spaces in navbar buttons to fit Google behaviour
for tablets (Nexus 7, Nexus 10).

PS2: Better values after some testing on Nexus 7
PS3: Previous solution isn't good

Change-Id: I1ea9c883c519641fd99a033a54a1dc29fd9d57bd
Signed-off-by: kecinzer <kecinzer@gmail.com>

Conflicts:
	packages/SystemUI/res/layout-sw600dp/navigation_bar.xml
	packages/SystemUI/src/com/android/systemui/statusbar/NavigationBarView.java