Issue: Eliminate the VW3>4 UpgradePath

As we have noticed in recent VaultWiki 3 > 4 upgrades, the process is not really reliable. As an upgrade is not an easy action to undo, we should completely remove the upgrade-path for versions < 4.0.0 Alpha 1. Instead, VaultWiki 4 should be installed as a separate product (which could automatically disable VaultWiki 3), and the import system should be used instead. If there are issues, an import can be executed multiple times until it's right while minimizing data loss. This cannot be accomplished with an upgrade.

Of course the version numbers would not change.