Restore ^instant commands

By undoing part of my commit and allowing the ScriptEngine to do a fair
chunk of what it did before, but restricted only to ^instant commands -
injected commands still use the new system.

Also, add some documentation to ScriptQueue functions and clean the
queue debug output a little
Add ~run: Wait the ran script to complete before continuing!

Utilizing a simple Java Runnable for a callback.
Also clean a last bit of debug.
Merge pull request #640 from mcmonkey4eva/master

Pull request for ^command ~prefixes