Bug 17792: Add opac_editable and opac_display methods

Bug 17792: Add opac_editable and opac_display methods

This patch adds two methods to the Koha::Patron::Attribute:

- opac_display
- opac_editable

Both method just check the corresponding Koha::Patron::Attribute::Type
and return the values for those attributes. This is useful to avoid
checking that manually on the controller scripts.

To test:
- Run:
  $ prove t/db_dependent/Koha/Patron/Attributes.t
=> SUCCESS: Tests pass!
- Sign off :-D

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>