Imported Upstream version 2.4
Merge tag 'upstream/2.4'

Upstream version 2.4
update changelog for 2.4
drop lintian overrides for space-in-std-shortname-in-dep5-copyright and wildcard-matches-nothing-in-dep5-copyright; lintian got fixed
drop/update patches
adapt the packaging to the new library soversions
generalize ffmpeg.lintian-overrides with wildcards
add debian/missing-sources with the sources of the minified CSS files in the upstream tarball
create the minified CSS files during package build
update debian/copyright
prepare for new upload