Hygiene: The big skin cleanup

By exposing a way to add to template data in core
a lot of our skin code disappears magically

Note: Toggling does not work in the desktop version of
the Minerva skin. This is a known problem and being addressed
separately.

Change-Id: I43fc26bf334753b189e20921f142bade7658ac31
Dependency: I0a9a7f10ea6a2e9c90c2a83e7c5f7fa56fa0fb93