Build PhabricatorTagView

Summary:
Builds out most of the non-hover-stuff from overview-hovercards.png. Things I didn't build:

• Tokens (I like them a lot but don't want to scope creep)
• Functions (backend mess / future work)
• Icons for tags.
• Tags with pointy ends and holes in them (an earlier mock had this I think but they're gone on final)
• The cyaney color for "Sporadic" since I just noticed it while typing this up.

Test Plan: Looked at UIExample page.

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2089

Differential Revision: https://secure.phabricator.com/D4029