Add options to the math tag

* id: Allows to name equations
  and deep link to equations
* forcemathmode: Allows to override the user defined rendering mode.
  This feature is useful for help pages and discussions about rendering.
* type: support for MathML and asciimath input
  required for MediaWiki instances that want to
  incorporate MathML sources like for instance pubmed

Change-Id: I615c7f1a5762e9e662937b70953fb873309d4c07