Feature activity stream

[tobyspark]

Implement activity streams. Provides a remodelled profile page, tweaked home page and activity admin functions.

Motivation

• rework existing activity functionality (e.g. profile page) to be comprehensive and easily extensible
• provide activity information for users (e.g. homepage's "Hello user" can have relevant info) and for admins (e.g. so Bob can see what's going on)
• provide framework for further functionality, e.g. has something I commented on had any more comments.