Math Node Matcher

This patch creates two files handling math node matching,
which are:
ve.dm.MWMathNode.js - a basic version of toDataElement
and toDomElement functions work
ve.ce.MWMathNode.js - math formulas in VisualEditor are
clickable and render as img tags

Change-Id: Ib909c5fb02e385c88050f42d02d207ab6a97d0dd
Math Node UI

Show an inspector with inputwidget when the user clicks a math
node. The data of the math equation is shown in the
edit box, it can re-render the math tag image when
the inspector is closed, and save the change when
saving the page.

TODO:
* Change the icon from link to math
* Translate title by translatewiki in i18n
* Other further UI improvements

Change-Id: I4d7533af25186cc39cc4bc6a4326d222ffd6db19
Merge changes I4d7533af,Ib909c5fb

* changes:
  Math Node UI
  Math Node Matcher