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 next year.

---

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.

There are a couple of things I want to do on this branch:

1. Deduplicate records.
   The effect of not doing this can be seen in the study locations
   sidebar, which assumes structural identity of StudyLocations.  This
   could be special-cased, but I think it's better to just apply that
   principle to all records.

   Record instances will have the natural key (type, id, rev).  They'll
   live in a Store, though our conception of a Store will be much more
   limited than what Ember Data provides.

2. Deduplicate code.
   The introduction of a Store should help this, though I definitely
   will have to be careful to not turn the Store into a waste dump.