Create and use activities

[Jessica Tallon]

Pump.io uses activities to represent when you post, comment, etc. We need to start storing the activities and using them on the feed API. This will involve introducing a new model and making it so commenting, deleting, uploading, etc. via either the API or the webUI creates and saves an activity.

[Jessica Tallon]

This is being worked on in my ​905-activities branch. There are two things left to do:

• Add to, cc, bto, bcc which are many to many relations between Users and Lists?
• Possibly refactor some of the methods on Activity to mixins?
• Can ​this be done any better?

[Jessica Tallon]

I believe this is now ready for review as of ​2d606f. There are two things which are known problems:

• ActivityIntermediator.TYPES doesn't allow plugins to support activities. (#962)
• to/cc/bto/bcc is not supported (#963)

Those two issues have been given their own issues.

[Christopher Allan Webber]

This looks good generally, though I haven't tested it yet. Jessica and I talked further, the main thing holding this back right now is we want to get the Python 3 branch merged first... I'm going to look at that next week.

[Jessica Tallon]

This has now been merged as of ​9a1fc42.