Simplify subcollections

This is not ready to be merged.  I have made a few changes that may not jive with the front-end.

A JSON root is being used by rails so that javascript can implicitly know when there are zero sub collections.

```js 
if (response.collections.length == 0) {}
```

Also, I'm unsure what issue the error handling was targeted at.  If a collections subcollections no longer exists but is still stored in the database it's a data integrity issue and should be addressed at a level lower than the application consuming it.

Here's the approach I would take:
1) Narrow down to the specific area where the errors are most high risk
2) Add begin rescue statements around that block
3) Have the javascript process the response code and display a generic error message if necessary.  That's possible to do globally with jQuery's AJAX implementation and a growl-like notification plugin.
4) Monitor production servers with New Relic app monitoring