Updated squareup libraries

The big change is in OkHttp from 1.3 to 2.1.
A few API changes regarding caches required code changes.
See https://github.com/square/okhttp/blob/master/CHANGELOG.md
for full list.

Also remove explicit entry for support-v4 since it's
transitively included through the appcompat-v7 dependency.
That way we don't accidentally have incompatible versions
of those two.

Change-Id: I0b2532276c72757e5941aef63cfc2f2dea8445ad
Merge "Updated squareup libraries"