Bug 12133: Add requirements for guarantor and guarantee

Bug 12133: Add requirements for guarantor and guarantee

Add two requirements when registering a new patron:

- A child patron must have a guarantor. This is controlled by
  a new syspref ChildNeedsGuarantor.
- A guarantor cannot be a guarantee.

Test plan:
1. Add a child patron without guarantor or child patron with guarantee
as guarantor succesfully.
2. Apply this patch.
3. Add a child patron as a guarantor.
=> Error is raised.
4. Turn syspref "ChildNeedsGuarantor" ON.
5. Add a child patron without a guarantor and error "Child needs a
guarantor" is raised.
6. Add guarantor. Guarantor can either be existing patron or added with
"Contact" section.
=> Save without errors.

Also prove t/db_dependent/Koha/Patron.t

Sponsored-by: Koha-Suomi Oy
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>