Map MenuItems to ViewPager tabs correctly in RTL

Also improved the handling of the mContactsUnavailableFragment in RTL.
The tabs still don't work perfectly in RTL for mContactsUnavailableFragment,
but this isn't a regression (and proved very tricky to solve without
changing the design). I'll file a bug for the remaining work after
checking this in.

Bug: 18011426
Change-Id: I695018464625f3f8329a33882d2d728f61c3b110