402120: Add support for rendering math in WikiText editor

* Initial (working) version with MathJax.
* Fix handling of MathJax source when not running under Eclipse.

Change-Id: Ica9d4e7d008a44199dff0895e35bd1d681132b5a
Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=402120