Bug 7154: Modification in borrower attributes

Bug 7154: Modification in borrower attributes

* group some attributes for a more friendly display

* allow a link between a borrower category and an attribute to display
  it only for the specified category

* Attr classes filled with AV 'PA_CLASS' category (you have to create AV
  with a new category 'PA_CLASS' to fill class list)

this patch add 2 fields in borrower_attribute_types :
    category_code
    class

Signed-off-by: Julien Sicot <julien.sicot@gmail.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>