Bug 27946: Article request fee methods in Koha::Patron

Bug 27946: Article request fee methods in Koha::Patron

This patch adds article_request_fee() and add_article_request_fee_if_needed() methods to Koha::Patron.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Patron.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>