Added SuperScript step for JSR-223 Script Engines in PDI

This is meant to be an improvement on (and/or replacement of) the PDI (experimental) Script step. This plugin offers many more capabilities, such as:
   - Drop-down UI for selecting the scripting engine
   - Allows non-compilable JSR-223 scripting (such as AppleScript)
   - Enables the use of the script's returned value as an output field
   - Enables use of the script as an input step (doesn't need a trigger)

Example KTRs are here: https://pentaho.box.com/s/jgjn64ejgzd9fbp2yd5y

One of the example KTRs (itunes.ktr) will play music while you wait for the transformation to finish (if you run on a Mac of course ;)