Delete invalids links

My plugin create world and destroy them after a certain time, this modification is needed to clean the MCPATH from this obsolet worlds.

I added a checkLink in the "world backup" routine, cause for the same reason, some worlds are created while the server is running, I dont add this change in this pull, cause I assume its an personnal adjustment :D, but you could add too cause some plugins use creation on the fly too (multiverse-like).