feat(main): Add support for pulling down docker containers

add an endpoint to pull down a container from the docker registry.
feat(docker): add ability to specify container to pull
feat(docker): use the tag store

this gives us the ability to look up an image later by a friendly
name.
feat(docker): spin up containers from docker image

this puts down a container from a docker image. It puts it in
/var/lib/containers/<name>
fix(docker): use img not image in copyAll

This little error made it so that only the top level image got copied
over. Now all layers are copied into place.

Also, ddd some logging to ease debugging.
feat(flags): add flags and ability to control paths

this adds flags for controlling the port and paths that systemd-rest
binds to. Now you can test with ./systemd-rest -p 8080 -D ./
fix(docker): we must walk the history backwards

WalkHistory walks from newest to oldest, we need to copy the layers from
oldest to newest. Ooops!
fix(*.go): run go fmt on all of the code
fix(docker): don't return early

Two bugs causing this loop to return too soon. Testing with multi-parent
VM now.
fix(docker): off by one error

Wow, this is sort of embarassing. Fix a off by one in the reverse
iteration.