fix typos: </math>, zeta, omicron, and tidy layout

Hi Daniel

Rather liking the look of your Moodle MathSlate editor! Am in the process of 'tweaking' it to work with the MathJax mhchem extension for editing chemical equations. Should be putting this onGitHub shortly.

Whilst doing this noticed a few typos in the config.json file and also tidied up the layout (to help my understanding).

Please review and patch these, as you see fit ;-)

Happy New Year!

Geoff