Add cp command and copy api endpoint to copy container files/folders to the host

The `cp` command and copy api endpoint allows users
to copy files/folders from a containers filesystem to the host.

The syntax for the command came from #382 mirroring scp.

CLI Command:

    docker cp 9be9a765dd28:var/log host/logs

API Endpoint:

    POST /containers/4fa6e0f0c678/copy HTTP/1.1
    Content-Type: application/json
    {
        "Resource":"test.txt"
    }

Closes #382