shell: Fix layout of container images sidebar in lower resoultions

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Fix layout of container images panel in lower resolutions

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Leave some space for the cpu column

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Avoid clipping the container cell buttons

Closes #1537
Fixes #1525
Reviewed-by: Stef Walter <stefw@redhat.com>