Simplify daemon management: "phd start"

Summary:

• Merge CommitTask daemon into PullLocal daemon. This is another artifact of past instability (and order-dependent parsers). We still publish to the timeline, although this was the last consumer. Long term we'll probably delete timeline and move to webhooks, since everyone who has asked about this stuff has been eager to trade away the durability and ordering of the timeline for the ease of use of webhooks. There's also no reason to timeline this anymore since parsing is no longer order-dependent.
• Add phd start to start all the daemons you need. Add phd restart to restart all the daemons you need. So cool~
• Simplify and improve phd and Diffusion daemon documentation.

Test Plan:

• Ran phd start.
• Ran phd restart.
• Generated/read documentation.
• Imported some stuff, got clean parses.

Reviewers: btrahan, csilvers

Reviewed By: csilvers

CC: aran, jungejason, nh

Differential Revision: https://secure.phabricator.com/D2433