Dashboard activities wiring

[michaelbrooks]

This connects the activities front end to the API and database.

Completely new things:

• BB activities collection that pulls the 10 most recent activities
• filled in BB activity model that links itself up to its associated user (provided by the server as nested data)
• tests for the entitylinks helper

Changes:

• changed activities database schema, adding ref_id field which contains the id of some object important to this activity. The exact interpretation depends on the activity type. The json_data field is still used for flexible storage (e.g. number of messages coded).
• the ref_id is converted into a ref_obj during retrieval from the database.

After we merge this, if you have already been running test copies based on the dashboard branch (which includes the activities table migration) you'll need to force the activities table to be recreated:

• drop the activites table in your database
• edit the migrations table to change the version number to 10
• redeploy (ant). activities will be recreated.

[michaelbrooks]

Just added some additional tests in service of issue #75