Upgrade to CSS4J 0.20

Version 0.14
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- API CHANGE: Refactor of user-agent classes. The sample DOM4JUserAgent has 
  initial support for cookies and HTTP Basic authentication.
- API CHANGE: DeviceFactory is a new abstraction that supplies style databases
  and other media-related objects. DeviceFactory.setStyleDatabase takes two 
  arguments, the first one being the medium for which it is intended. Then, 
  the database used by the style declarations changes according to the current 
  target medium, as set by the XHTMLDocument.setTargetMedium method unless the 
  style declaration is stand-alone, in which case the style database for the 
  DeviceFactory's default medium will be used.
- API CHANGE: Removed method XHTMLDocumentFactory.setDefaultStyleSheet, which 
  was deprecated in previous version, to avoid confusion.
- API CHANGE: DOMMediaList.getLength() now returns 0 when it contains "all". 
  A media list with "all" is considered equivalent to an empty media list.
- API CHANGE: CSSStylableElement.getStyle returns an empty style instead of a 
  null when there is no inline style defined.
- API CHANGE: Cleaned the CSSStyleSheetFactory methods. The parse method has 
  been removed; instead, use the parseCSSStyleSheet method on any style sheet.
- Cleanup in the CSS implementation classes.
- Support for alternate style sheets. See the methods enableStyleSheetsForSet, 
  getStyleSheetSets, getSelectedStyleSheetSet and setSelectedStyleSheetSet in 
  CSSDocument.
- Added the method getOverrideStyle to CSSDocument, matching the DocumentCSS 
  DOM Level 2 interface.
- Added the getStyleSheets method to CSSDocument, matching the DocumentStyle 
  DOM Level 2 interface.
- Improved CSS error handling.