Add basic math editing features

This solve [bug 945228](https://bugzilla.mozilla.org/show_bug.cgi?id=945228).

**Note**: This is based on @fred-wang's [Javascript (La)TeX to MathML parser](https://github.com/fred-wang/TeXZilla) that has a [Firefox Add-ons](https://addons.mozilla.org/en-US/firefox/addon/texzilla/) that have been revised already.

This add a [plugin for CKEditor](https://github.com/r-gaia-cs/CKEditor-TeXZilla) that add basic math editing features based on (La)TeX input.

You can test it [here using kuma's version of CKEditor](http://www.ime.unicamp.br/~ra092767/ck3.html) and [here using CKEditor4](http://www.ime.unicamp.br/~ra092767/ck4.html).

There are at least two "minor bugs" that are related with kuma's version of CKEditor. You can find more information about it [here](https://github.com/r-gaia-cs/CKEditor-TeXZilla/issues/1) and [here](https://github.com/r-gaia-cs/CKEditor-TeXZilla/issues/2).