web: Implement slider for choosing a container memory limit

This implements the memory row as described by the mockup here:

https://github.com/cockpit-project/cockpit-design/blob/f1d6e8c560d6230bad24e4ac11c8916dc75d9e52/docker/docker-run-hires.png

The only difference is that the total memory is not shown, as the
container is not actually being allocated a portion of the memory. This
is about setting a limit.

Fixes #295
Closes #353
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
web: Implement CPU priority slider

This is done on a logarithmic scale. Defaults to 'default' priority.

Fixes #296
Closes #353
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
web: Reset CPU and Memory limit check boxes in run dialog

Reset the check boxes whenever the page is displayed for consistent
behavior.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
agent: Don't poll when interval is zero, as documented.

Closes #359

Reviewed-by: Stef Walter <stefw@redhat.com>
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