Add 'vertical-align': 'middle' to iFrame.
Remove \( and \) in dialog.
Copy styles from iFrame to body inside iFrame.
Make math class configurable.
Add MathJax to preview.
Add truncated MathJax library.
Remove old hacks from preview: for IE, Chrome (#8016) and Firefox (#9047).
Add configuration option allows to use local MathJax lib.
Change CDN to load only TeX parser (without MathML).
Updates only first <head> in preview.