Add alternate locations in the config

[funnyboy-roks]

Add the ability to add alternate locations in the configuration file. These locations probably need to be limited to those running bytebin instances, since we'd have to heavily change how the program interacts with the apis.

This can probably be done by copying the UrlSet struct to be used in the config.

I'm not sure how the user would specify which location to download from, probably just a --from <location> flag in the cli, but if you have any ideas, I'd appreciate your input.