R1:d13a3225634c

Clean up Maniphest transaction rendering a bit more

Summary:
Ref T2217. This partially retreads the ground from D7115.

- We're rendering silly transactions about descriptions when creating tasks. Hide those.
- Move the "created" transaction back to status. This fixes two things that are otherwise more of a mess than I'd anticipated:
- It fixes Reports without making a mess (see <https://github.com/facebook/phabricator/issues/395>).
- It renders old transactions properly (i.e., "created"…