Bug 13852 - Manage C4::VirtualShelves in C4::Auth for performance

Bug 13852 - Manage C4::VirtualShelves in C4::Auth for performance

In C4::Auth there is a use C4::VirtualShelves.
Virtualshelves are displayed in all OPAC pages, but not in intranet.
For performance, we should move this into a require only for opac pages.

This patch adds a condition to fetch virtualshelves only if opac and moves the dependancy on C4::VirtualShelves into require calls.

On my desktop, I have those compilation times for C4/Auth.pm :
- Without patch : 0,41 seconds
- With patch : 0,22 seconds

This performance improvement is very usefull for pages that only use a few as dependancy, like errors/404.pl

Test plan :
- Be sure there are some public lists
- Apply patch
- Go to opac (not logged-in)
- Click on "Lists"
- Check you see the public lists
- Login with a user
- Be sure this user has some private lists
- Click on "Lists"
- Check you see the public and private lists
- Logout
- Go to /cgi-bin/koha/opac-reserve.pl
- You see the loggin page
- Click on "Lists"
- Check you see the public lists
- Go to intranet
- Check you can loggin

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>