CasesInstance -> StudyLocation.
Eliminate Pancakes.localStore.

We don't need it just yet.
Set up an EventSearch-StudyLocation association.

This makes it possible to save study locations with event searches;
that, in turn, matters because the scope of a search (any command,
really) is part of that command's identity.

As part of this change, StudyLocation's ID is now the URL of the Cases
instance that serves it.
Show study selections selected for search.

This is the first non-trivial bit of behavior in this application.
Expect integration tests soon.