Disable the "Edit Project" button for users without edit permissions

Summary: Self-explanatory.

Test Plan: Viewed the project page as a user without edit permissions and saw the link greyed out.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D13255