mcoffline v2000.0.0

Welp I showed henry the first version of this program, feeling all proud
at how fast I finished it, and he pointed out that the program doesn't
actually convert the playerdata folder.... It's not really particuarly
useful without doing that.

So, introducing MCOFFLINE 2000. Give it a path to a whitelist.json and
it'll create a whitelist.json.offline and in your world folder a
playerdata.offline folder too!