Adding Ponder-related files.

Summary:
Ponder is similar in spirit to the Wiki tool, but uses a Q&A
format and up/downvotes to signal user sentiment. Popular
questions are moved to the top of the feed on a 5-minute
cycle based on age (younger is better) and vote count (higher
is better).

Pre-apologies for noob diff.

Test Plan:

• ./bin/phd list Should include PonderHeatDaemon; phd launch it if necessary.

• Navigate to /ponder/ ; observe sanity when adding questions, voting on them, and adding answers.

• Confirm that questions and answers are linkable using Q5 / Q5#A5 formatted object links.

• Confirm that searching for Ponder Questions works using built-in search.

Feedback on code / schema / whatever organization very welcome.

Reviewers: nh, vrana, epriestley

Reviewed By: epriestley

CC: gmarcotte, aran, Korvin, starruler

Differential Revision: https://secure.phabricator.com/D3136