Activate the new Repository creation workflow

Summary:
Ref T2231. This:

• Activates the new multi-step workflow, and exposes it in the UI.
• Adds "can create", "default view" and "default edit" capabilities.
• Provides a default value for repository.default-local-path and forces repositories into it by default. It's still editable, but Phabricator gets it correct (for some definition of correct) by default now.

Test Plan: Created some new repositories with the new workflow.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1286, T2231

Differential Revision: https://secure.phabricator.com/D7413