Add hosting, serving, and push policy options to repository edit

Summary:
Basically straight from D7391. The differences are basically:

• Policy stuff is all application-scope instead of global-scope.
• Made a few strings a little nicer.
• Deleted a bit of dead code.
• Added a big "THIS DOESN'T WORK YET" warning.

Test Plan: See screenshots.

Reviewers: hach-que, btrahan

Reviewed By: hach-que

CC: aran

Maniphest Tasks: T2230

Differential Revision: https://secure.phabricator.com/D7416