web: Consistent debugging and waiting state for docker operations

Expand the functions in DockerClient for each of the level docker
REST actions. Add create(), rm(), rmi().

Add better debugging to all the operations and pages. Enable one of
these in the javascript console:

$cockpit.debugging="docker"
document.cookie="debugging=docker"

Update the waiting state consistently for all actions on images
and containers.

Closes #361
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
web: Replace action buttons on details page when already doing something

If already performing an action on a container, then replace the
action buttons with a throbber.

Besides being much clearer that something is happening, we're able
to prevent error conditions that would result from running multiple
incompatible actions on the same container.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>