Payment input view

[LeHack]

This view should allow to add information of a received payment from a particular group member.
Possibly we could have a clickable list (with group selection above) of group members (those who have pending payments highlighted somehow or moved higher up the list). Upon clicking a set of controls would emerge allowing to specify the payment (type and amount, defaulting to the current setting for payment type, see #11 ). After saving the indications should refresh.

ℹ️ Note: The model will be prepared as part of #1 so this information will be available regardless whether #11 is done.
ℹ️ Note 2: This was finally omitted in the current model implementation. Due to time restrictions, it will be part of a future update.