Configure MathJax when it's loaded by XBlocks in studio
Configure MathJax when it's loaded by XBlocks in studio

When using RequireJS, MathJax was configured in an `init` function
in the RequireJS config. With the switch to Webpack and $script,
that configuration needed to be moved to the dynamic loading done by
$script.

[EDUCATOR-3160]

appsembler/edx-platform,angelapper/edx-platform,ahmedaljazzar/edx-platform,ahmedaljazzar/edx-platform,cpennington/edx-platform,EDUlib/edx-platform,msegado/edx-platform,philanthropy-u/edx-platform,a-parhom/edx-platform,angelapper/edx-platform,eduNEXT/edx-platform,edx-solutions/edx-platform,msegado/edx-platform,appsembler/edx-platform,arbrandes/edx-platform,jolyonb/edx-platform,EDUlib/edx-platform,edx/edx-platform,ahmedaljazzar/edx-platform,jolyonb/edx-platform,edx/edx-platform,eduNEXT/edx-platform,arbrandes/edx-platform,ESOedX/edx-platform,angelapper/edx-platform,msegado/edx-platform,eduNEXT/edunext-platform,cpennington/edx-platform,mitocw/edx-platform,stvstnfrd/edx-platform,teltek/edx-platform,eduNEXT/edunext-platform,arbrandes/edx-platform,edx/edx-platform,jolyonb/edx-platform,ESOedX/edx-platform,EDUlib/edx-platform,stvstnfrd/edx-platform,eduNEXT/edunext-platform,cpennington/edx-platform,mitocw/edx-platform,msegado/edx-platform,stvstnfrd/edx-platform,appsembler/edx-platform,arbrandes/edx-platform,edx-solutions/edx-platform,philanthropy-u/edx-platform,ahmedaljazzar/edx-platform,edx-solutions/edx-platform,teltek/edx-platform,appsembler/edx-platform,a-parhom/edx-platform,edx-solutions/edx-platform,philanthropy-u/edx-platform,mitocw/edx-platform,edx/edx-platform,teltek/edx-platform,angelapper/edx-platform,philanthropy-u/edx-platform,stvstnfrd/edx-platform,eduNEXT/edx-platform,EDUlib/edx-platform,cpennington/edx-platform,jolyonb/edx-platform,a-parhom/edx-platform,ESOedX/edx-platform,msegado/edx-platform,a-parhom/edx-platform,eduNEXT/edunext-platform,ESOedX/edx-platform,teltek/edx-platform,mitocw/edx-platform,eduNEXT/edx-platform