This PR allows you to use the pay button generator to create buttons that target apps. This means that you can generate an invoice that is linked to an item on the POS/Crowdfund (targeting the item is optional). The POS/Crowdfund item amount -> invoice creation amount validation works too so that the user cannot modify the amount of a perk using just html ( fixes#1392 )
* Need to reference Microsoft.EntityFrameworkCore.Design else you can't generate migrations
* fix design time migrations issues
* update snapshot
```
Your startup project 'BTCPayServer.Data' doesn't reference Microsoft.EntityFrameworkCore.Design. This package is required for the Entity Framework Core Tools to work. Ensure your startup project is c
orrect, install the package, and try again.
```
*
