REGISTRAR, CORE: fixed parsing common name

CORE

- Parse parts of common name only if matcher.find() returns true.
- This cause method to return map with "namePart"=null on no match
  instead of throwing an exception.

REGISTRAR

- Added checks to call parseCommonName() only on non-empty and != null input.
- Do not overwrite "displayName" to "Shib-Person-displayName" as attribute
  name to get from federation values.