Add similiar questions sidebar to Ponder

Summary: Ref T9099. Testing out a two column layout in Ponder, with the main idea being creating a more browsable, discoverable product. I'd like the side column though to be a little smarter and provide project based searching. Ideally, if I'm reading Resolved Maniphest questions, other Resolved Maniphest questions are likely interesting. Another scenario is if I'm answering questions, in which case browsing more Open questions would also be interesting. Ponder "Main Column" still needs to be redesigned.

Test Plan: Browse open questions, resolved questions.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T9099

Differential Revision: https://secure.phabricator.com/D13849