Provide helpers to easily perform escaping with wiki syntax

It's currently very tedious to perform a proper syntax of some elements in XWiki, and so we should provide helpers to ease life of developers and avoid vulnerabilities in our code.

Some helpers that are needed:

• capability to escape labels of wiki links (double escape)
• capability to escape wiki syntax used with a translation:

  ## Example of creating a link from a translation like "translation=my {0}link label{1}
  #set ($myLink = $services.localization.render('translation', ["__BEGINLINK__", "__ENDLINK__"]))
  #set ($myLink = $services.rendering.escape($myLink, "xwiki/2.1"))
  #set ($myLink = $myLink.replace($services.rendering.escape("__BEGINLINK__", "xwiki/2.1"), "[["))
  #set ($myLink = $myLink.replace($services.rendering.escape("__ENDLINK__", "xwiki/2.1"), ">>$linkTarget]]"))
  $myLink