NoSuchMethodError on pre-1.13 servers when joining a course with scoreboard enabled.

The RegisterNewObjective method has changed on 1.13 (extra argument). To be compatible with <1.13 servers, need to use the deprecated RegisterNewObjective method.

Also the message "Not completed yet" is > 16 character limit, which prevents the scoreboard being displayed and causes an IllegalArguementException on the console. This again only applies to pre-1.13 servers.