Added MathJax javascript lib to layout.

[siad007]

That would give us the ability to have MathML inside descriptions like:

    /**
     * Standard constructor.
     *
     * <math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
     *   <mi>P</mi>
     *   <mo stretchy="false">(</mo>
     *   <mi>E</mi>
     *   <mo stretchy="false">)</mo>
     *   <mo>=</mo>
     *   <mrow class="MJX-TeXAtom-ORD">
     *     <mrow>
     *       <mo>(</mo>
     *       <mfrac linethickness="0">
     *         <mi>n</mi>
     *         <mi>k</mi>
     *       </mfrac>
     *       <mo>)</mo>
     *     </mrow>
     *   </mrow>
     *   <msup>
     *     <mi>p</mi>
     *     <mi>k</mi>
     *   </msup>
     *   <mo stretchy="false">(</mo>
     *   <mn>1</mn>
     *   <mo>&#x2212;<!-- − --></mo>
     *   <mi>p</mi>
     *   <msup>
     *     <mo stretchy="false">)</mo>
     *     <mrow class="MJX-TeXAtom-ORD">
     *       <mi>n</mi>
     *       <mo>&#x2212;<!-- − --></mo>
     *       <mi>k</mi>
     *     </mrow>
     *   </msup>
     * </math>
     *
     * @param string $name
     * @param int    $targets
     * @param string $configName
     */
    public function __construct($name, $targets, $configName)
    {
        // ...
    }