Bug 9032: add ability to accept list share invitations and remove shares

Bug 9032: add ability to accept list share invitations and remove shares

This patch handles:

[1] The response (acceptance) by the invited person.

If the person accepts this share, the private list of the sender will
be shown under Your lists on the shelves page. In OPAC 'Your private
lists' has been renamed to Your lists (just as in Staff). The Type
column shows Private or Shared for these lists; a list appears as
Shared as soon as an invitation has been accepted. The owner has the
options to Edit, Delete or Share; the invited person does not have
these options on the shared list.

[2] Removing an accepted share.

If a user accepted a share, they should also be able to remove it again.
The Remove Share button is visible on OPAC when viewing Your lists or
a particular shared list.

Note: AddShare has been extended to return a possible database error.
If the share invite could not be added, a mail will not be sent.

Test plan (for prog theme):
Enable pref OpacAllowSharingPrivateLists
User 1 creates new private list P1, perms: D-A-D, adds 2 items, sends share
User 1 checks your lists display: is P1 Private with Edit button?
User 2 accepts share: sees P1, but cannot add or delete items
User 2 checks your lists display again: P1 shows Shared without Edit?
User 1 checks your lists display again: P1 shows Shared with Edit?
User 2 tries to accept share again: should fail now
User 3 tries to accept share: should also fail
User 3 tries again, modifies shelfnumber and/or key in url: should also fail

User 2 creates new private list P2, perms: A-A-A, no items, sends share
User 2 checks your lists display: P2 shows Private with Edit?
User 1 accepts, adds one item
User 1 checks your lists display: P2 shows Shared without Edit?
User 2 checks your lists display: P2 shows Shared with Edit?
User 2 deletes item of user 1 (allowed)
User 2 deletes list P2
User 1 checks your lists display in opac or staff: P2 is gone?

User 1 creates private list P3, sends a share.
User 1 creates private list P4, adds one item, sends a share.
User 2 accepts the share for P3.
User 2 checks the shelves display, and removes share P3.
User 2 accepts the share for P4.
User 2 views shelf P4 with one item and confirms Remove share on that form.
User 2 checks shelves display again.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Dobrica Pavlinusic <dpavlin@rot13.org>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>