Workspace Chevron, fixes T151

Summary:
* adds a `.chevron` to workspace accordion menu

* changes `.active` state of icon

* reorganizes css

Test Plan:
* test floating layout in FF.
* test `.active` state

Reviewers: rjmackay, shadowhand

Reviewed By: shadowhand

Subscribers: dkobia, eyedol

Maniphest Tasks: T151

Differential Revision: https://phabricator.ushahidi.com/D72