Bug 14146: Add the ability to cumulate restriction periods

Bug 14146: Add the ability to cumulate restriction periods

At the moment the default behaviour is not to cumulate the restriction
periods but to apply the longest one.
This patch set creates a new syspref CumulativeRestrictionPeriods. If
on, the behaviour changes and the restriction periods are cumulated: the
days of the second restriction are added to the actual restriction
period.

We could add a new circulation rule instead of a syspref, but I am not
sure it's very useful to have such granularity for this behaviour (can
be changed if needed).

How it works:
Let's take 2 items, A and B.
A is returned with Na days late, and B Nb days late
The grace period is Ng and there is 1 day of suspension charge per day
of overdue
The suspension period is until day D = Na - Ng + Nb - Ng

I would have expected D = Na + Nb - Ng but it's how it worked before
this patch.

Test plan:
Create several overdue for a given patron
Do the checkins and confirm that the period are added if the pref is on.
If the pref is off, you should not get any changes in the existing behaviour.

Sponsored-by: Orex Digital
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>