XWIKI-18836: Links located in macros are not saved as backlinks

  * Provide a new LinkParser component whose jobs is to allow extracting
    links from an XDOM
  * Improve MacroRefactoring role to allow extract links from a macro
    content or parameter
  * Improve DefaultMacroRefactoring to parse macro content for
    extracting links
  * Improve IncludeMacroRefactoring to extract links from macro
    parameters
  * Refactor XWikiDocument to rely on LinkParser
  * Improve existing integration test to check with various links to
    ensure backlinks are created in each case (standard link, default
macro link, nested macro link, image link, include macro parameter)