Allow the browser to cache the images in the page editor (new images
will get new mappers and therefore update is not an issue), don't create
new image component by settings changes but update them to allow again
the browser to use the cached images.
Only set the mapper encoding if it's really found (in the case where it
is not defined by the configuration), don't set it with a default one,
use only the default to deliver the media resource if needed
