When renaming username/community, allow transfer period of redirecting to new one.

[lifenautjoe]

When someone renames a community or username, we should allow some time for the transfer to happen. During this period the old name should redirect to the new one.

[lifenautjoe]

Thanks @duichwer for this suggestion.

[duichwer]

Maybe public world posts with a link to this community could be updated, too. I know that we don't have this information right now, but as long as translation is possible for those posts, it would be okay in my opinion to update those posts. Maybe this should be discussed somewhere. And the rename feature would have to be locked that no one can DDOS the servers by renaming a community with many redirects...