Replace Ember Data with a custom store.

I'm sure Ember Data will in time become a fantastic library.  However,
presently, I've lost quite a bit of time in making persistence work with
the following (simple) scenario:

   EventSearch - 0..* --- 0..* - DataCollector

Similar multiplicities apply for EventType and StudyLocation.

The frustrating thing is that data _does_ reach the server; I just have
problems with the record lifecycle (see previous commit).  But even with
transaction micromanagement (i.e. adding all dirty records to a
transaction), I keep hitting those lifecycle errors.

Doubly frustrating: I can get this sort of thing to work in a test app,
but not here; the bad interaction is quite elusive.

I therefore have to conclude that Ember Data is indeed not production
ready in the most severe sense.  We'll check in every now and then; see
https://code.bioinformatics.northwestern.edu/issues/issues/show/3993.

---

This commit eliminates Ember Data and replaces it with a very rough but
working replacement.  The server-side behavior is unchanged.  The jQuery
uritemplate and linkheaders plugins are present because they're used for
parsing the Link: header.

All models now use "id" as their primary key; however, no keys were
removed.  This is why the DataCollector model was introduced, and why
EventType has both "id" and "local_code" attributes.