Create an internal activity stream feature to use for audit trails, and timelines

[mrchrisadams]

Creating a single activity stream to track behaviour would be useful in a number of places in the OneClickOrgs app.

In issue 94 it's referenced:

This is tricky because we don't have a 'real' notification system yet. The timeline is built by querying the database for existing records (members, proposals, etc.) and reconstructing the events out of the data it finds.

However, when a member resigns, the only record that's left in the database is that the member's 'active' field is marked as 'false'. So we're not saving: (a) when this happened; and (b) that this was a resignation rather than an ejection.

To solve this properly we need either a proper events log, or a better record of a person's membership history, both of which are fairly big jobs.

Also, when chatting to Chris Mear on IRC, it came up again here:

5:03 PM one thing i'm thinking about is that, on the master branch, we're already using state machines to manage most of the model transitions
5:03 PM and i've just started looking into something that will save an audit trail using that state machine system
5:03 PM which might feed nicely into a timeline system

I'm adding this ticket here to start collecting thoughts about it, and possible libraries we could use to provide this feature with.