Swarm mode modifications

[PabloRapidScale]

trafficstars

#72

• Added some lines to handle the way that Docker Swarm handles container names and tags. It should be able to handle both standalone docker and docker swarm.
• Added README section for swarm, to keep changes minimal the container should run in global mode so it looks up and backs up whatever local containers match the criteria.
• Changed the way the backup is saved to use a timestamp as a prefix to created dated backups. This can be ripped out if single file is preferred.