Add MetaData Block/Events to allow specifying meta data to XDOM/Listeners

Several use cases that already cause issues now:

• source name
  • to test right for script macros
  • to resolve include document name
• source syntax
  • to know how to re-parse macros like box, script, etc. when a page containing a macro in some syntax is included in a page using another syntax
  • when the syntax inside the generated macro are not the same as the source syntax like in xwiki/1.0 parser which internally convert content to xwiki/2.0 syntax before using xwiki/2.0 parser