Rewrote this project.

Attension

Incompatible with previous version!!
Please delete the ServerManagerForBungeecord folder!!
And I haven't written the document yet, so use the previous version until the document is complete.

What was fixed?

・If the server did not start properly, we could not connect to the server until the proxy is restarted.
・This plugin used too much resources. (maybe)
・The proxy couldn't be restarted if the server did not start properly.
・If we were using Bungeecord, we got an error about slf4j.