Bug 27699: Add register information to responsive staff interface header menu

Bug 27699: Add register information to responsive staff interface header menu

This patch adds register information to the version of the header menu
shown when the browser width is narrower.

To test, apply the patch and enable the UseCashRegisters system
preference.

- If necessary, create at least one cash register for your library under
  Administration -> Cash registers.
- From any page in the staff interface you should see a menu in the
  header showing your username and logged-in branch.
- Expand the menu and choose "Set library, desk and register."
- Select a cash register and save.
- The cash register information should now appear in the header menu.
- Narrow the width of the browser until the menu collapses and shows
  only a user icon.
- When you expand this version of the menu you should see the
  currently-suggested register.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>