Allow Maniphest tasks to be edited from the list view

Summary:
Fixes T1945. Ref T2947. At various times, installs (Disqus, Dropbox, etc.) have asked for a way to edit tasks more quickly. Provide edit-from-lists.

{F44700}

{F44701}

The one rough edge on this is that if you change the task priority we update it inline but don't move it. It's probably infeasible to actually move it, but maybe we could give it some sort of visual style to indicate that it's dirty.

Test Plan: Edited tasks normally and via this action thing.

Reviewers: chad, btrahan

Reviewed By: chad

CC: tido, deuresti, ahoffer, aran

Maniphest Tasks: T1945, T2947

Differential Revision: https://secure.phabricator.com/D6086