Adjust action bar tab policies

Action bar tabs now stack in portrait mode on all screen sizes rather
than display embedded. This only affects apps with a targetSdkVersion
of JB or greater, as older apps may not be prepared for the different
measurement of the bar or have an appropriate stacked bar background
drawable.

Stacked action bar tabs now have a width limit. This prevents
super-wide tabs that can span the whole screen. The cluster of tabs
is centered if it does not span the full width.

Add ActionBarPolicy to give a single point to query for various action
bar measurements and behaviors that vary with configuration.

Change-Id: I01162ca009c14f6f0e712fc906b9db6382c738cd