[super] Activity Streams

[seanh]

We want to add github-like "activity streams" (chronological lists of events) to CKAN.

Etherpad: ​http://ckan.okfnpad.org/notifications (most relevant parts inlined here)

Tasks

1. New domain objects Activity and ActivityStream? [2d] #1298

2. Migrate existing data into activity streams model [3.5d] #1510

3. Generate activity events when objects are saved [4d] #1298 (Further tickets are needed for generating activity events from objects other than packages and resources, e.g. users.)

4. Get the activity stream for a given user as a list of Python objects. [1d] #1511

4a. Get activity streams for packages, groups, tags, sets of multiple sources that users subscribe to, etc.

5. Render a user's activity stream on her user page [3d] #1494 #1496

5a. Render activity streams for packages, groups, tags, sets of multiple sources that users subscribe to, etc.

5b. Render activity streams as RSS feeds, as JSON via an API call, etc. #1495

6. Enable users to subscribe to activity streams

7. Deploy to UAT [0.5d]

8. Docs and announce [1d]