bundle: audit commit author/messages

[erichanson]

• split up commit.message and commit.description, message should be varchar(255), description should be text. do we want to use markdown here? probably.
• since PostgreSQL roles don't have email, it's unclear how to record who made a commit. we can use endpoint.user, but bundle doesn't require that endpoint be installed, so figure out what to do when it isn't
• fix the commit UI (which needs a lot of work) to handle the above