Custom scripting 🎉

[binaryoverload]

🎉 The feature we've been waiting to implement.

Scripting will be based on the Rhino JS engine which allows us to lock down everything sufficiently. Everything non-vanilla Javsscript that we want users to be able to access will have a specialised class to pass in. Under no circumstances should any JDA object from the bot be directly passed in as that will give the user full control of the bot.