The videojs javascript is over 1MB of javascript which we don't need to
load on every page, now that we only require it demand, the js can be
lazily loaded when its needed, which keeps the first.js smaller and more
likely to stay in browser cache.
The previously used minification libraries were:
a) Unmaintained
b) Had some silly licensing issues (MDL-36457)
The new library is smaller, maintained, active and GPL-compatible.
No changes from the upstream version have been made, it is recommended by
upstream to install these depdencies via composer - but the composer
installation is bundled with a load of test files, shell scripts etc (and
we don't use composer to manage 'production dependencies') so we have to
do it manually.