R1:5d6bb0ffebd2

Import raw GitHub event data into Nuance

Summary:
Ref T10537. Ref T10538. This polls the GitHub events API and creates Nuance items from the raw data.

It does nothing useful with them.

Test Plan:
- Polled GitHub.
- Saw some items get created.
- X-Poll-Interval seemed to work.
- ETag seemed to work.
- Recognizing when we hit items we've already seen seemed to work.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10537, T10538

Differential Revision: https://secure.phabricator.com/D15440