Controller's graphic instances are not synced to renderer

[jhobz]

The controller page does not validate its list of graphic instances with any source of truth. This can easily lead to out-of-sync behavior. Here are a couple reproductions to demonstrate this behavior.

"Stale graphic" repro steps:

1. Upload graphic to server, open renderer.
2. Select graphic from dropdown and load graphic to renderer.
   a. Note graphic instance ID (should be 1)
3. Press load again to load new instance of the same graphic.
   a. Note graphic instance ID (should be 2)
4. Try to clear (or any operation) original graphic, instance ID 1, observe error in log and clear fails (because the instance doesn't actually exist).

Screenshot (with graphic instance IDs of 7 and 8):

"Lost control" repro steps:

1. Upload graphic to server, open renderer.
2. Select graphic from dropdown and load graphic to renderer.
3. Play graphic instance.
4. Reload controller page.
5. Observe that the list of graphics instances is now empty, leaving no way to clear the current graphic from the renderer.