Bug 2093: (follow-up) Add OPAC dashboard for logged-in users

Bug 2093: (follow-up) Add OPAC dashboard for logged-in users

This patch adds some additional markup for applying styles to and the
corresponding CSS.

Also modified: Links to opac-user.pl should now open the correct tab.

To test, apply the patch and compile the modified LESS file. Clear your
browser cache if necessary. Follow the original test plan and confirm
that the revised links work correctly.

Signed-off-by: Hugo Agud <hagud@orex.es>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>