Add commission model

[morremeyer]

We should have a commission model where we can combine multiple orders for one team into a commission.

Features:

• Multiple orders for a team can be combined into a commission
• Future: Create QR codes for commissions so that they can be put onto Ready-To-Pick-Up commissions. The helpdesk shall be able to scan that QR code to mark a commission and its related orders as Completed.

Fields:

• OneToMany: orders -> Which orders are in this commission
• Boolean: handed_out -> If the commission has been handed out. When setting a commission to handed_out, handed_out_to and handed_out_by has to be specificed.
• Char: handed_out_to: Who has picked up the commission?
• Char: handed_out_by: Who handed out the commission?