Make Multimeter sample browsing UI a bit more useful

Summary: Ref T6930. Just iterating on this a bit: add some column grouping stuff so you can slice results apart and figure out where they came from.

Test Plan: {F389632}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T6930

Differential Revision: https://secure.phabricator.com/D12626