Added 'Agents' to the event model
Javascript agent model saving on the server
Fixes createdBy and lastEditedBy properties.

The first person to edit an event without these properties will end up being attributed as The Creator. Lump it.
Renamed 'role' as 'explainer', as people around the business seem to like that word
Added read-only agents to the view models
Merge branch 'master' of github.com:guardian/frontend-admin into agents

Conflicts:
	app/views/events.scala.html
Display the number of agents associated with the event
Merge pull request #68 from guardian/agents

Read-only agents