Provide a HandleDocumentWorkflow SCXML implementation using Groovy for expressions and functions

The new HandleDocumentWorkflow is handle based, so the SCXML context will be more generic.
It thus also doesn't have to 'adjust' the state representation depending on for which document variant or hippo request child node of the handle like needed for the existing document workflow implementations.

As SCXML can use Groovy for expressions and scripting, it also will be possible to use more expressive constructs, custom functions, etc. within the SCXML document itself (initial script).