R1:b63eb09cacf1

Don't require a callsign to set a repository's local path

Summary: Ref T4245. When creating new repositories, set a default local path based on the repository ID instead of callsign.

Test Plan:
- Created a new repository.
- Saw it get a reasonable, ID-based local path.
- Edited a repository to make sure the `applyFinalEffects()` wasn't doing anything whacky.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D15303