Fixed download again

You can download the file now from spigot since my jenkins server stoped working.

- Added the help message when you only type /cs
- fixed messages for 1.15+

- Added help message

Added multi world support for commands and heads.

Changed to Java 8, cause it's the most common jre/jdk used, and it should still work with newer java versions

- Updated download url

- Added Multiworld support
- Messages are now editable in the config.yml
- Set amount of heads a player needs to find in the config.yml