js/loader: disable click handler block on refresh

This used to be ways too slow when many elements where involved. Left
the old code there as a reminder. In case we really need it we should
use something faster like an overlay or so.
js/loader: trigger 'beforerender' container event
js/loader: support multi-container redirection

Redirections to #!-separated URLs (multiple containers) should also
work when not re-rendering the whole layout.