Add dashboard showing project and task info for current user

We have about 10-15 projects now and have many users that are involved in multiple projects. Under such conditions we ran into some inconveniences in particular it's somewhat difficult to effectively manage one's tasks across multiple projects. This is a proposed solution - to have a user-centric "dashboard" page that shows links to a user's projects, combined activity feed of all that user's projects minus his own actions, list of user's assigned tasks across all his projects, and activity feed of that user's assigned tasks only.

We've been running with this for awhile now and think it's valuable. It'll also partially address issue #242 . I haven't gotten to writing tests for the new functions I introduced yet, but I figure it'd be good to try to get this in first, I'll try and follow up with some tests if this gets merged. I'm also thinking of adding an option to allow setting this dashboard page as default landing page after login.