Several changes:

- added an extension point to register a default test suite for a 
  file extension
  
- if a suite is registered for a file extension, the XPECT_SETUP 
  section becomes optional
  
- inside the XPECT_SETUP section, the cross reference to the 
  test suite is now syntactically optional
  
- added support for system properties "xpectFiles" and "xpectBaseDir".
  they can override what has been specified via an 
  @XpectTestFiles annotation
  
- improved naming of launch configurations when .xt-files or 
  XPECT-statements are executed.