Added Run Script step for JSR-223 Script Engines

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
    - Removal of JavaScript-specific code (the Modified Java Script Value step is the alternative, although this step does support the JavaScript scripting engine)
    - Allows non-compilable JSR-223 scripting (such as AppleScript)
    - Enables the use of the script's returned value as an output field

Example KTR is here: https://pentaho.box.com/s/ixmnnp6qiqo5jpmamvwm