Add tagging capability for projects

[celrae]

Would love to see the addition of a tagging tool; @jcn and i have discussed, but for other readers: lots of chapters are interested in non-funding ways to support applicants, and allowing chapters to flexibly add tags to projects would help us more easily sort and follow up with applicants in bulk.

To be specific: In NYC, we see a lot of folks looking for space, e.g.; being able to send them a list that we have on file of places to find free/cheap space for your awesome project would be nice — and being able to review and tag projects with "needs space" would be helpful. Would maybe be most relevant for chapters like NYC that regularly get 120+ monthly applications.

Originally posted by @celrae in #386 (comment)