Migrate project blurb/description to standard custom field storage

Summary: Ref T4379. Major goal here is to remove ProjectProfile so all edits use ApplicationTransactions. This also makes things more flexible, allowing users to disable this field if they don't like it.

Test Plan: Ran migration, verified data survived, edited/created projects, reordered fields.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4379

Differential Revision: https://secure.phabricator.com/D8182