GitLab

Also:
- Split entity viewer redux state into smaller parts, one of which is sidebar
- Added the sidebar part of entity viewer redux state,
   modelled as an object keyed by genome id.
- Added a pair of statuses (OPEN, CLOSED) to the Status enum
   and used it to denote whether sidebar is open or closed.

Also:
- Use a dedicated component for sidebar tabs rather than generating them in
   StandardAppLayout.
- update npm script for running the style linter
- update test for ZmenuContent component (use mock redux store rather than real one)
- make browser bar content (gene info) responsive to the width of its container
   (via ResizeObserver)
- make opening and closing of the sidebar to be instantaneous rather than animated
  (better for performance)
- remove viewport metatag in the hope that the site will display in its desktop version 
   on mobile devices

Add a common grid-like layout to be shared by different applications (e.g. Genome browser
and Entity viewer)