activity 5.x-3.0-beta

Complete rewrite of the module done by Robert Douglass with the help of sirkitree.

New features:
- Extensible architecture so that any module can integrate with the Activity API
- Role and action sensitive messages so that you can tell the sender of a message "You sent Bob a message" and the receiver "You've received a message from Jim"
- Table view of all activity and "My activity"
- RSS feeds for all activity and "My activity"
- Integration with nodes, comments and user relationships.
- Simpletest unit testing of core get/set API functions
- All messages are customizable via the admin interface with token support provided by Token module