Implement Code Reuse#38

Currently script listeners have no way to share code between them. Many of my listeners use the same functions copy/pasted between them. It would be extremely valuable to be able to be able to reuse code.

This does seem to be the same as #33 . This feature would be very useful for our company too since we also reuse the same methods in many scripts. A concept similar to Script Variables where I can define functions to reuse would be great.