Bug 33242: Allow passing add_{duration} options to KohaDates

Bug 33242: Allow passing add_{duration} options to KohaDates

For example, if I want to add a few days to the issuedate in a
TT template, I could do this:
    [% checkout.issuedate | $KohaDates add_days => 3 %]

This development allows you to pass add/subtract years, months, weeks,
days, hours, minutes and seconds.

Test plan:
Pick a notice like CHECKOUT.
Add a line like:
    [% checkout.date_due | $KohaDates with_hours => 1, add_minutes => 15 %]
Do a checkout. Verify that the notice generated contains a time that
shifted 15 minutes.
Undo your change.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>