Bug 27779: Group payouts by type of debit they're applied against

Bug 27779: Group payouts by type of debit they're applied against

This patch adds additional grouping to the cashup summary output such
that payouts are additionally grouped by the types of debit they're
applied against.  The cashup sumary modal is adapted to expose the
descriptions at the grouping level too.

Test plan
1/ Add a various transactions using a cash register (Using Point of
Sale, Patron Accounts with payments etc).
2/ Refund some of the debts and pick the 'cash' option for payout.
(ensure you pick a variety of debit types)
3/ Add some credit to a patron account, (either refund a debt as
'credit' or add a 'manual credit')
4/ Payout the credit as 'cash' on the patron account
5/ Cashup the register
6/ Inspect the cashup summary for your cashup.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>