R1:b43eb5aa7c20

Add transaction-oriented editing to projects

Summary:
- Make some editing operations transaction-oriented, like Maniphest. (This
seems to be a good model, particularly for extensibility.) I'll move the rest of
the editing operations to transactions in future diffs.
- Make transaction-oriented operations publish feed stories.

Test Plan:
- Created a new project.
- Edited an existing project.
- Created a new project via quick create flow from Maniphest.
- Verified feed stories publish correctly.