R1:7b334f37bd38

Improve tag support in Diffusion

Summary:
- When viewing a commit, show its tags.
- For commits with many tags, show a list of all tags on the tag list interface.
- Improve some handling of symbolic references.
- When tags contain content, show it on the browse view reached by clicking the tag name.

Test Plan: Looked at commits with and without tags, clicked "More tags...", clicked tag names.

Reviewers: btrahan, vrana, davidreuss, jungejason

Reviewed By: btrahan

CC: aran

Maniphest Tasks…