TNL-1677

TNL-1902

This reverts commit 4a086f54.

When cdn is down specially in the country like china
and others user face problem as application doesn't
work as intended. Instead of making mathjax hard
dependecy I have converted it into soft dependey
so that it won't cause user problem to use application
smothly if mathjax is not present.

TNL-1498

When mathjax is down discussion forum doesn't work
as we were using markdown.js with processor as
mathjax. Unavailability of mathjax raise error in
js which stops discussion to render. So I made
markdown independent of mathjax. Markdown now will
use mathjax when it is available otherwise ignore it.

TNL-1149

Several IE bugs have been fixed in 2.4.

Move vendor javascript into common/static/js/vendor, so that they can be shared between the CMS and LMS, and create an html template that includes all of the vendor js needed for the courseware

generated when Check is clicked)

main.html now includes mathjax_include for all mathjax stuff
problem.js refreshes mathjax formulas on change
all previous *_fromjs renamed to *_dynamath, eg textline_dynamath

to show quickedit when settings.QUICKEDIT is True.  add
mathjax_include.html because that is needed by quickedit.html