Allow running the previous version of a DApp

[dbadol]

Current situation: When a new version of a DApp is available, the user is informed and forced to update it. They cannot ignore the new version and keep using the previous one for a while.

However, updating a frontend is a big deal (cf. security risks, phishing, hacks, etc.) and should only be done once the content of the new version has been verified.

Solution we propose: When informed about the new version, the user should have the option to ignore it ("Remind me later") and keep using the one it currently has locally (i.e. the previous version).