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.
Previous commits were overlooked, they should have passed the
system context to filter_manager::setup_page_for_fitlers(), the
page context was passed instead. Regardless, the processing of
the latter is too excessive for what we need, but, more importantly,
it does not return "Off, but available" filters which we also need.