add fallback platform to retrieve installer version

[moehreag]

This allows the installer version to display correctly even on platforms we don't have a native installer for (e.g. Android)

Other changes:

• Recognize "arm" to also point towards an aarch64 architecture for linux (technically not 100% correct but the closest we have; and 32-bit arm devices are getting increasingly rare, especially those running full desktop linux)
• don't show the installer version if despite the fallback platform we couldn't get the version from the maven
• remove the unused platform parameter from getLatestVersion