Give unit test results their own table in Differential

Summary: Ref T10457. This gives unit test results a more first-class treatment in the Differential UI, and consolidates some rendering code.

Test Plan:
Before:

{F1135536}

After:

{F1135537}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10457

Differential Revision: https://secure.phabricator.com/D15365