Introducing the asset of type file creation. This involves making a
node collection entry of type asset, as well as a file collection
entry, plus all the needed variations if such file is an image or a
video. Further, depending on the storage backend (pillar or other) we
synchronise the files there using rsync. Currently this functionality
is available only via pillar-web, since a web interface is needed to
upload the file in a storage folder, which is shared between the two
applications.
