B-48943 - Update api-validator configuration to match translation when configuration xsl-engine

Updating the Config objec to accept the following
- select XSD engine as "Xerces" or "SaxonEE"
- select XSL engine as "Xalan", "XalanC", "SaxonHE" or "SaxonEE"

Deprecated the following
- Config.setUseSaxonEEValidation
- Config.getUseSaxonEEValidation
- Config.useSaxonEEValidation
B-48943 -  Update api-validator configuration to match translation when configuration xsl-engine

- Updating Config to accept "Saxon" for xslEngine to maintain compatibility
- Adding tests to verify Config object maintains backward compatibility
B-48943 - Update api-validator configuration to match translation when configuration xsl-engine

- Updating Config object as per Jorge's requests.
Merge pull request #162 from usnavi/xsd-engine

   B-48943 - Update api-validator configuration to match translation when configuration xsl-engine