Upgrade Phabricator task create URL

Summary:
/maniphest/task/create doesn't work anymore, as forms are now configurable,
and Phabricator violates http://www.w3.org/Provider/Style/URI.html.

New URL is to create a task is /maniphest/task/edit/form/1, as it's use
the form #1.

Test Plan: test URL

Reviewers: dereckson

Differential Revision: http://devcentral.nasqueron.org/D156