Add CLI parameter to validate X3ML resources

[ymark]

Add CLI parameter to validate X3ML resources

[ymark]

A new parameter was added to the CLI options of the X3ML Engine. It is

--validate  (or -d)

If that parameter is specified, then instead of transforming data, it just validates that the provided X3ML mappings resource is valid with respect to X3ML XSD Schema (collected from the corresponding -x parameter).

If the X3ML mappings resource is valid, then an OK message is returned (in the standard output), otherwise an exception message is thrown in standard error