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)
I'd like some design input on this as well. It'll probably mean that each location entry field will become an auto-suggest.
It will also make one-off imports slightly more complicated