Warn the users when a valid app url that is not an official safe app is used

[JagoFigueroa]

Description

We should warn the users if an opened app is an "unknown" one.

When a valid url is used to open an app but this app is not part of the list of official apps or a custom one added by the user (with the manifest check) a disclaimer should be shown to notify that it is not part of our ecosystem and can lead to undesired issues.

To make it less annoying for the user, show the warning only once per custom app URL (save in the localStorage).