finance/nextcloud-cospend: Add nextcloud app cospend

Add Nextcloud Cospend 💰

Nextcloud Cospend is a group/shared budget manager.
It was inspired by the great IHateMoney.

You can use it when you share a house, when you go on vacation with friends,
whenever you share money with others.

It lets you create projects with members and bills.
Each member has a balance computed from the project bills.
This way you can see who owes the group and who the group owes.
Ultimately you can ask for a settlement plan telling you which payments
to make to reset members balances.

Project members are independent from Nextcloud users.
Projects can be accessed and modified by people without a Nextcloud account.
Each project has an ID and a password for guest access.

MoneyBuster Android client is available in F-Droid and on the Play store.

PayForMe iOS client is currently being developped!