Some quick code to get EmbeddedTabs to work. This is mostly throw-away.
Tab apps to the menu.
added todo
Merge branch 'EmbeddedTab' into ExternalIFrameTab

Conflicts:
	apps/admin.py
	apps/plugin_renderers.py

Also made view_tab to call get_renderer_class and added that method to EmbeddedTab too.
Added get_renderer_class for EmbeddedTab
Merge branch 'EmbeddedTab' into ExternalIFrameTab
CAUTION: Schemamigration! Simply adding new model. Forgot this from the commit where the model was actually implemented.