Fix permission check for "Create Task" on workboards

Summary: Fixes T9090. You don't need to be able to edit a project to create tasks on its workboard. Being able to view the project is sufficient, and the user certianly can if they got this far.

Test Plan: Viewed workboard, hit "Create Task".

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9090

Differential Revision: https://secure.phabricator.com/D14015