Detect existing channels and roles | Don't delete everything

[merlinfuchs]

So right now the bot destroys the entire server and rebuilds it. While this is great, it probably uses alot of resources and time to do this. Instead Xenon should be smart enough to tell what roles, channels, and categories are identical to the incoming backup being loaded and leave them alone, thus generating/backing up messages that exist in the new backup.

https://gitlab.com/magicbots/xenon_pu/issues/21