Attach annotations to discourse parts

[cbogart]

The schema allows for annotations to be attached to things other than contributions (users, discourse_parts, etc) but currently that's not being done because there's no affordance to browse that data.

• Add column syntax for adding these to CSV import files
• Allow optional querying of discourse_part and user annotations in the browser

Longer term:

• Hover over item in list of discourse_parts to show annotations specific to it. Maybe add a glyph to indicate they are present

[cbogart]

The tree view of discourse parts could be a treetable kind of thing with optional details: http://ludo.cubicphuse.nl/jquery-treetable/

Or the main grid could have an alternate view of discourse parts (with attributes) instead of contributions.