Support XPath 2.0

[nuest]

The server should support both transformation descriptions in XPath 1.0 and 2.0.

• add (optional) XPath version property to transformation files (defaults to 1.0)
• add configuration for XPath 2.0 engine (maybe (!!!) replace service-loader based configuration, though that might be fine for the default still)
• add unit tests

{
   "transformationDescription":{
      "name":"transformerSML20",
      "applicabilityPath":"boolean(//*[local-name()='SensorML'][@version='2.0'])",
      "xpathVersion": "2.0",
      "namespaceMappings":[