Add support for '--sticky' (or whatever) flag on decking attach

[makeusabrew]

If present - or perhaps, by default - this should take note of when a container goes away and then quietly try and re-attach when it comes back. I hate having to stop and restart the attach when a container is restarted. For now it can poll but we should be able to use the events endpoint.

[makeusabrew]

This is now the default behaviour but needs some finessing, that's for sure!