Organisational units, series, events and groups

Pretty massive PR including:

Organisational units:
 * CRUD
 * Getting / Adding / Deleting series from an organisational unit
 * Getting the organisational unit tree

Series:
 * CRUD
 * Adding / Deleting events to/from series

Events:
 * CRUD


It's pretty rought, but I'll go do some self-review (which hopefully gets in before @nicolaasmatthijs gets on the plane)
Needs the

```
* @param {Object} callback.err An error that occurred, if any
* @param {Object} callback.body The JSON response from the REST API
* @param {Response} callback.response The response object as returned by requestjs
* @see gh-series/lib/rest.js for more information
```

everywhere