🚧 add a donation screen

[Simon-Laux]

Apple AppStore provides the possibility to add a donation screen as "In-App-Purchase".
To complete thie PR following steps are needed:

• connect bank account with AppleDeveloper account
• finish the UI to provide screenshots
• register in-app-purches with generated screenshots
• finish api communication for purchase subscription and managing subscriptions

Show a donation screen instead of just a link where there are 2 links, one for money donation and one
for time donation (basically contributing). The section with the money link is replaced by
inAppPurchase-donation options on macOS appstore builds/releases.

[farooqkz]

I haven't got a Mac so I can't test this.

[Simon-Laux]

does not work yet anyways, also it's not only for Mac, outside of Mac it should show links. anyways this is probably sth for 1.48 or later

[Simon-Laux]

The design mockups I made to explain the idea:

in Appstore:

outside of appstore, where we don't have the restrictions that forbid us from using our donation link:

[Simon-Laux]

this pr is not relevant anymore. also we don't really have enough macOS appstore users to justify the work of adding inApp purchases for them.