Split Repository EditEngine form into smaller pages

Summary:
Ref T10748. This allows an EditEngine form to be broken up into pages.

This is less powerful than PHUIPagedFormView, because the pages are not sequential / stateful. Each form saves immediately once it's submitted, and can not take you to a new form or back/forward in a series of forms.

For example, you can't create a workflow where the user fills out 5 pages of information before we create an object, like the current repository workflow does.

However, the only place we've ever wanted to do this is repositories and it's fairly bad there, so I feel reasonably confident we aren't going to miss this in the future.

(We do "choose a type of service/repository/rule -> fill out one page of info" fairly often, but can do this without the full-power paging stuff.)

Test Plan:

• Created a repository usin the new Manage UI, filling out only a handful of fields.
• Edited a repository using the new Manage UI.
• All forms are now EditEngine forms offering paged views of the big huge underlying form:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10748

Differential Revision: https://secure.phabricator.com/D15832