Add PDI Extension Point scripting plugin

This set of extension point plugins allows the user to write scripts in JavaScript, Groovy, etc. that will be called as extension point functions. For example, the user can write a script called TransformationStart.groovy and it will be executed when a transformation starts. All the extension points (up through 5.2) are supported.

Two examples (TransformationStart.groovy and TransformationFinish.js) are included to show that the two engines that come with PDI (Groovy and Rhino-JS, respectively) can be used to run scripts as execution point methods.