Implemented Phrequent time tracking functionality.

Summary:
This differential implements Phrequent's time tracking
functionality for users and hooks it up to Maniphest. It
also includes a basic "Time Tracked" list for the Phrequent
application, where users can review what they've spent time
working on.

Test Plan:
Apply the patch and track some things in Maniphest. They
should appear in the "Time Tracked" view of Phrequent.

There is also a phrequent.show-prompt option which toggles
whether to display a prompt when tracking time. I'm unsure
of whether the prompt is useful or is more likely to cause
people to click "Track Time", go off and do the task and then
come back to the prompt still waiting for them to confirm. A
potential solution to the "accidentally clicking the button
and recording 2 seconds of time" might be to show a prompt
on stop if the total time is under 10 seconds, asking whether
the user wants to keep or discard the tracked time.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2857

Differential Revision: https://secure.phabricator.com/D5479