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