Bug 15407: Koha::Patron::Categories - replace GetBorrowercategory

Bug 15407: Koha::Patron::Categories - replace GetBorrowercategory

The purpose of C4::Members::GetBorrowercategory was to return the patron
category for a given categorycode. This can be done easily with the
Koha::Patron::Categories->find method.

Test plan:
- Same prerequisite as before
- Edit a guarantor and confirm the information will be updated for his/her
  guarantee(s).
- Update a child to adult patron (Note: Should not we hide the patron
  categories limited to others libraries? If yes, it must be done on another
  bug report).
  There is a special behavior if there is only 1 adult category, the
  user does not need to select a category. So the same as before with
  only 1 adult patron category.
- Import a patron with a category_code which does not exist. You should
  be warned.
- Modify some patron using the batch patron modification tool. The
  patron category descriptions should correctly be displayed.

Note that the overduerules page has already been tested in a previous
patch.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>