R1:a90daf5d3048

Add very basic item rendering for GitHub events, parse IDs + URIs

Summary: Ref T10538. This extracts and renders URIs for GitHub events so we can link to the original thing on GitHub.

Test Plan: {F1186332}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10538

Differential Revision: https://secure.phabricator.com/D15505