Summary:
- Looks better (can probably still use some tweaks), especially search.
- Moves logout from weird footer location to main menu.
- Reactive: on tablets and phones, the menu adjusts to remain useful.
- Fixed position on desktops for future side nav changes.
- Adds an icon header thing that's currently hard-coded but will be application-driven soon.
Test Plan: Used menu on desktop, tablet, phone, logged in / logged out, toggled darkconsole. Will add some screenshots.
Reviewers: btrahan, chad
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T1569
Differential Revision: https://secure.phabricator.com/D3105
