TOPIC: Allow viewing project trees by topic

I'd like to be able to see all my projects in the Projects tree sorted by topic

So lets say that I've got the topics
Personal
Family
Business
Education
Hobbies

Then I'd like to see all of my projects broken down into those groups rather than having everything lumped under "Projects" the way it is now.



It would probably make sense to look at replacing the current Topic and Priority system with some kind of tagging system as was suggested here earlier this month.

That way I can tag a project "trip across country" as Personal, Family, and Education



It might get confusing as I would expect that "trip across country" in a Project tree sort would show up under each tag (meaning it's on the list 3 times) but I could work with that pretty easily.