Store list of old realm paths to redirect to new ones after a path_segment or parent change?

[LukasKalbertodt]

There are two actions that invalidate old links:

• Changing the path segment of a realm
• Changing the parent of a realm

Both invalidate all links to that realm, all its descendants and all videos mounted in any of those realms. That's bad and the UI should warn of this hazard appropriately. But of course, there is another way: somehow store the old paths as well so that we can redirect to the new links. This is what GitHub does when you rename a repository.

I think having this would be quite an advantage as otherwise, everyone is basically stuck with the realm tree fairly quickly (considering you don't want to invalidate links). However, there are also disadvantages, of course:

• Adds complexity and more data to the DB
• What if a another realm then tries to change the path to the old path? THEN the link would finally be invalidated. So we just postpone it and have to show the warning then.