filters, for images: start with untagged/tagged boolean

This is a new feature and flag. (replaces the suggestion of a flag for
--untagged images).
The concept is to have a syntax to filter. This begins with this
filtering for the 'images' subcommand, and at that only filtering for
whether images are untagged.
  example like: docker rmi $(docker images -q --filter 'untagged=true')

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
filters: remove out filter proc prototype

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
filters, for images: docs

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
filters: cleanup & fmt

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
images filter: remove the redundant inverted filter

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
images: fix markdown documentation

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
filter flag: split out for separate --filter flags

adding tests and allowing for easy passing of filters.Args from client
to server.

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
server: very debug.

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
filters: change untagged to dangling

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
filters: use json marshal, instead of beam/data

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
filters: don't encode an empty set. update comments

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
filters: don't encode empty set. API docs

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Merge pull request #4430 from vbatts/vbatts-images_orphan

Adding -f untagged=true flag to `docker images`