US19 // items - add soldForPrice when sold

Value Proposition

As a user I want to set a price i sold the item for so that i can keep track of sales

[x] on items-page on each item-card there is a button called verkauft...
[x] button opens a popUp with input to enter a number
[x] on popUp there are two buttons: abbrechen + bestätigen
[x] abbrechen closes the popUp with data unchanged
[x] bestätigen will add the entered number to items data
[x] entered number gets displayed on item-card
[x] also Gewinn gets calculated depending on actual sellingPrice and gets displayed on item-card

[x] create branch feature/us19/item-add-soldForPrice and switch into it
[x] use or create popUp-component with buttons
[x] create button on itemCard to open up the popUp
[x] add function to edit soldForPrice value for this specific item
[x] render real VK: + calculated Gewinn on item-card (Gewinn now is real, not calculated with targetPrice anymore)