Make the expression evaluator understand variable names with namespaces

[MarkusFrankATcernch]

BEGINRELEASENOTES

• Make the expression evaluator understand variable names with namespaces
  • Variable names containing a : or :: are now accepted by the expression evaluator. This is first step towars resolving Using a colon for a variable passed to DD4hep Evaluator: "namespace:name" rather then "namespace_name" #421
  • It has now to be seen what has to be done further. The DCMS example was not yet updated to use this feature.
• Add new example in examples/ClientTests to test this functionality.
  ENDRELEASENOTES