R1:cdcd49e4eece

Revising Flag UI

Summary:
Re-adding side nav (feels less spacy now).

Replaced header with crumb. Looks nicer with the filter imo.

Test Plan: {F38201}

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5517