Projects - merge create + edit interface code paths

Summary:
Fixes T6145, T4016.

Filed T6287 and T6288 for some polish on this.

Test Plan: Made new projects from Maniphest - great success. Made new projects from project / create - also great success.

Reviewers: chad, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T4016, T6145

Differential Revision: https://secure.phabricator.com/D10679