Bug 20912: Rental Fees based on Time Period

Bug 20912: Rental Fees based on Time Period

Some libraries would like to be able to charge a rental fee based on the
number of days an item will be checked out, as opposed to the flat fee
currently offered by Koha.

Test Plan:
1) Apply this patch
2) Run updatedatabase.pl
3) Edit an itemtype, add a daily rental fee of 1.00
4) Check an item of that itemtype out for 7 days
5) Verify the patron now has rental fee of 7.00

Signed-off-by: Matha Fuerst <mfuerst@hmcpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>