Tasks can be defined in the commit message (Phabricator part).

Summary:
Phabricator did not support giving the task ids in the commit message.
Currently there is no default implementation for this, but there is a
Facebook specific implementation. At some point default implementation
for Maniphest tasks to revisions will be added.

Test Plan:
Tested with the Facebook specific implementation that task ids are
recognized in the commit message and tasks are automatically attached
to revisions.

The task attached to this revision was added from the commit message.

Reviewed By: jungejason
Reviewers: jungejason, epriestley
CC: dpepper, edward, gpatangay, tuomaspelkonen, jungejason
Differential Revision: 240996