Bug 18228: Table revision of virtualshelves

Bug 18228: Table revision of virtualshelves

In order to make the permissions easier, we will replace the columns
allow_add, allow_delete_own and allow_delete_other by two new columns
allow_change_from_owner and allow_change_from_others.

The distinction between adding or deleting an entry is no longer made.
If you have change permission, you can do both. Also deleting an entry
does no longer depend on who added the entry.
Formerly, the owner could always add entries. It is now possible to
make a list readonly.

We will not use the combination of owner=no and other=yes. This will
leave us three possibilities:
[1] owner=no, other=no: The list is read-only. No one can change
    contents of the list. Naturally, the owner can edit permissions.
[2] owner=yes, other=no: Only the owner can change contents.
[3] owner=yes, other=yes: Anyone seeing the list can change contents.
    This especially applies to shared lists and public lists.

The two database columns will be presented in the interface as one
permission field offering the three abovementioned options.

Test plan:
[1] Run the db rev.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jesse Maseto <jesse@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>