Bug 14544: Add Koha::Virtualshelf and Koha::Virtualshelves

Bug 14544: Add Koha::Virtualshelf and Koha::Virtualshelves

The 2 modules C4::VirtualShelves and C4::VirtualShelves::Page are really badly
coded and buggy.
It became complicated to fix and enhance them.
This rewrite will make the code more robust and the list feature will be easier
to change.

Some new modules are added to the Koha namespace (Koha::Virtualshelf,
Koha::Virtualshelves, Koha::Virtualshelfshare[s] and Koha::Virtualshelfcontent[s])
to take advantage of Dbix::Class.

The patchset fixes some bugs:
1/ Bug 6279 - Can't delete lists from the second page of lists in the OPAC
2/ The owner of a list should not need any permission to remove content from
his lists.
3/ No feedback messages when actions are done

Test plan:
A) Intranet and OPAC
1/ Create more than 20 private and public lists with different users
2/ Edit some and confirm that the changes are taken into account
3/ Share some lists with other users
4/ Add / remove contents
Be sure you have some lists with more than 20 items (to test the pagination)
5/ Play with permissions and confirm it works as expected.
For private lists:
They should not be viewed by anyone else, if they are not shared
If they are shared (OPAC only):
a. "Allow anyone else to add entries"
  Should allow the user with whom the list is shared to add entries.
b. "Allow anyone to remove his own contributed entries."
  Should allow the user with whom the list is shared to remove his own entries.
c. "Allow anyone to remove other contributed entries."
  Should allow the user with whom the list is shared to remove any entries.

For public lists:
They should be viewed by anyone else.
a. "Allow anyone else to add entries"
  Should allow any user to add entries.
b. "Allow anyone to remove his own contributed entries."
  Should allow any user to remove his own entries.
c. "Allow anyone to remove other contributed entries."
  Should allow any user to remove any entries.

6/ Download and sent lists.

7/ Confirm that the "Add to" feature works as expected.

8/ Confirm that the "Add an item to" works as expected.

9/ Delete some lists.

10/ Print some lists and subscribe to the RSS feed (OPAC only) (with more than
20 items).

11/ Use the remove "Remove share" links.

Signed-off-by: Alex Arnaud <alex.arnaud@biblibre.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>