Pause/freeze containers during commit

Initiates a pause before committing a container,
adds a pause option to the commit command, defaulting to 'true'.

Fixes #6267 
Fixes #3675

Docker-DCO-1.1-Signed-off-by: Eric Windisch <ewindisch@docker.com> (github: ewindisch)
@ewindisch you need to bump the API version to 1.13