Import Apps in Automatic Update Mode

At the moment, when you import an app from a remote repository (and later Google Play), a stand-alone copy is created that has no more connection to the original app.

The idea is to provide a checkbox when importing an app that sets the app to automatic update mode where (for now) all manual changes are blocked and all app data is automatically updated when it changes in the remote repository. This includes adding new APKs automatically to the app when their availability is discovered by repomaker.

Later, we might want to apply the Automatic Update Mode only to certain parts of the app (e.g. update the APKs, but not the description and screenshots), but this is just mentioned and not part of this ticket. The first iteration of this feature will be an all or nothing Automatic Update Mode.