Complete the CommonHTML output

This is a meta-issue.

• add webfonts support
• #1035 (closed) improve fractions
• proper stretchy characters
• stretchy embellished operators
• support mtable attributes
• variable-width mtable elements
• #968 (closed) add mlabeledtr support
• TeX versus MathML spacing
• allow mtextInheritFont
• support mathsize attribute
• match font heights
• support displayAlign and displayIndent
• support line breaking
• bevelled fractions
• handle hrefs, class, and other attributes
• support maction
• support menclose
• support ms
• support mglyph
• support mphantom
• support mmultiscripts
• handle VCENTER TeXAtom
• add isMathJax to created nodes
• handle zoom action
• update web fonts
• https://github.com/mathjax/MathJax-dev/issues/11 create new combined configurations with CommonHTML as default
• Fix font displayed in the About MathJax box.

What else?