Added MySQL support, switch to MySQL by setting
AccountSys: MySQL

LockLogin will migrate automatically yaml players data to MySQL when they join, to migrate MySQL data to Yaml, simply use /ll migrate

Since now, when the plugin loads, if the server is not bungeecord, all the online players will be kicked with the message
"Your session with the server has expired"
That for the players know that hey have to login and to avoid errors if MySQL is enabled and you load the plugin with third-party plugin loaders, like plugman