reorganize /recordings JSON response

I want to start returning the pixel aspect ratio of each video sample
entry. It's silly to duplicate it for each returned recording, so
let's instead return a videoSampleEntryId and then put all the
information about each VSE once.

This change doesn't actually handle pixel aspect ratio server-side yet.
Most likely I'll require a new schema version for that, to store it as a
new column in the database. Codec-specific logic in the database layer
is awkward and I'd like to avoid it. I did a similar schema change to
add the rfc6381_codec.

I also adjusted ui-src/lib/models/Recording.js in a few ways:

* fixed a couple mismatches between its field name and the key defined
  in the API. Consistency aids understanding.
* dropped all the getters in favor of just setting the fields (with
  type annotations) as described here:
  https://google.github.io/styleguide/jsguide.html#features-classes-fields
* where the wire format used undefined (to save space), translate it to
  a more natural null or false.

ui-src/lib/views/RecordingsView.js

@@ -256,13 +256,14 @@ export default class RecordingsView {
    *
    * The data is expected to be an array with recording objects.
    *
-   * @param  {String} recordingsJSON JSON data (array)
+   * @param  {object} recordingsJSON JSON data (object)
    */
   set recordingsJSON(recordingsJSON) {
     this.showLoading = false;
     // Store as model objects
-    this._recordings = recordingsJSON.map(function(r) {
-      return new Recording(r);
+    this._recordings = recordingsJSON.recordings.map(function(r) {
+      const vse = recordingsJSON.videoSampleEntries[r.videoSampleEntryId];
+      return new Recording(r, vse);
     });
 
     const tbody = this._element;