Raised min sdk to 11 as loaders only go back to 11

At some point considering 10 might make sense, for now that requires
more work than benefit.
Added navigation drawer

Lots of work still to be done, but basics are working now.
Remove unused gcm.xml
MainActivity retains current nav position on config change
Moved about from MainActivity to AboutFragment
levels: loader is no longer called twice in ChooseRiverFragment
levels: list will be refresh when navigating back to fragment