SWITCHYARD-1314 Message Validator improvement

Contains:
 - https://issues.jboss.org/browse/SWITCHYARD-1315 - Return Details of Message Validation Error
   -- validate() method returns ValidationResult object, which has getDetail() method to return error details when validation fails
 - https://issues.jboss.org/browse/SWITCHYARD-1257 - Support multiple Schemas in XmlValidator
   -- added SchemaFiles element in validate.xml to specify multiple schema files and removed schemaFile attribute
   -- XmlValidator now supports namespace aware validation as well with setting 'namespaceAware' attribute as true
 - https://issues.jboss.org/browse/SWITCHYARD-1312 - Add XML Catalog support to XML Validator
   -- added SchemaCatalogs element in validate.xml to specify multiple schema catalogs