Moved overlay.js.coffee to core/ as all roles need to use it

Also, added MathJax to student layout
Merge branch 'master' of https://github.com/abhinavc/web-application
Forgot into include MathJax
Show wide-X - not wide-wait - to students seeing report-cards
Load version-0 as preview for students and teachers

This is a temp. measure. Going forward, they will see solution to
just the version the student received
Encode & decode TeX during decompiling and loading respectively ..

Symbols like + do not transmit well over the internet. They need to be
escaped first
Merge remote-tracking branch 'upstream/master'