Upgrade to CSS4J 0.42

Version 0.42
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 * Core:
- NSAC: a couple of small wording-style changes.
- NSAC implementation: add a missing @Override annotation.
- DefaultEntityResolver: allow retrieving remote resources with file ending 
  with ".mod" or the proper content type.
- DefaultEntityResolver: load HTML5 entities for XHTML strict and transitional 
  DTDs.
- DefaultEntityResolver: do not use an assumed publicId in getExternalSubset.
- DOM implementation: refactor for improved code readability and reusability.
- DOM implementation: introduce an XML-oriented DOMDocument.
- DOM implementation: add a generic XML DocumentBuilder.
- DOM impl.: createDocument() was not creating the document element when 
  requested.
- DOM impl.: methods of named attribute maps weren't correctly handling live 
  addition and removal.
- DOM implementation: fix a bug in Text.splitText(int).
- DOM implementation: fix NPE in Node.insertBefore().
- DOM implementation: fix several pending namespace issues.
- DOM implementation: allow namespaceless attributes.
- DOM implementation: fix a few attribute bugs.
- DOM impl.: Comments: Do not put additional space in toString() serialization.
- DOM implementation: initial support for changing Document's behavior via 
  strictErrorChecking.
- DOM impl.: transform HTML tagnames to lowercase in Document.createElementNS
- DOM implementation: more spec-compliant element serialization in toString().
- DOM impl.: CSSDOMImplementation.hasFeature now returns always true except for 
  "SVG".
- DOM implementation: implement getSchemaTypeInfo() in attributes.
- DOM implementation: do not attempt to return anything with 
  DOMDocument.getInputEncoding().
- DOM impl.: refactor to allow DocumentTypeImpl being used with other DOM 
  implementations.
- DOM impl.: DOMElementTest: remove unnecessary SAC parser configuration.
- Add getColorDepth and getPixelDepth to StyleDatabase, remove getBitsPerColor.
- Remove W3C's Screen interface, which provides information that this 
  implementation splits into CSSCanvas, CSSViewport and StyleDatabase.
- CSSOM: move two W3C interfaces from doc.style.css.w3c to parent package.
- CSSOM: have CSSMarginRule interface extend CSSDeclarationRule instead of 
  CSSRule.
- CSSOM: support custom properties ('variables').
- CSSOM: Shorthand setters and builders: clean up method visibility.
- CSSOM: OMCSSUnknownRule.java: add missing SPDX header information.
- StylableDocumentWrapper: refactor the handling of embedded and linked style 
  sheets.
- WrapperUserAgent: connect to resource before retrieving headers.
- Unit tests: better name for the HTML sample file.
- Unit tests: remove stack trace printing in selector parser NS tests.
- Unit tests: use the correct HTML5 doctype for the HTML sample.
- Update copyright notices to 2019.

 * Dom4j module:
- Small tweak to XHTMLDocumentFactory to be compatible with XMLDocumentBuilder.
- DOM4JUserAgent: connect to resource before retrieving headers.
- Unit tests: adapt to method name changes in core testing infrastructure.
- Update copyright notices to 2019.

 * Agent module:
- DefaultUserAgent: connect to resource before retrieving headers.
- Update copyright notices to 2019.

 * AWT module:
- Update copyright notices to 2019.