Merged in NRRPLT-8011 (pull request #113)

[NRRPLT-8011] Added xsd validation to the .exc
- The new xsd validator checks whether the ExDConfFile.xsd exists,
  if not throws a warning
- If .xsd exists parses the .exc based on the xsd schema
- Throws a warning if .exc is malformed. Intentionally does not stop the
  parsing as small errors in the .exc can be ignored instead of breaking
  the entire simulation.

Approved-by: Ugo Albanese
Approved-by: Stefano Nardo