Add local docker "registry"

[ipf]

When creating a new docker instance with ct docker:create the name of the instance and a unique identifier should bei written to a kind of local "registry" i.e. ~/.ct/docker-registry.json.
This may be useful to further implement a command such as ct docker:start {hash} or ct docker:start all or ct docker:list

[elmar-hinz]

I am also thinking of port management, to run multiple projects in parallel, without setting the ports by hand. Maybe in connection with a local DNS, to not bother with ports at all.

[josefglatz]

@elmar-hinz are there any scenarios where you work on 2 projects together? Or do you mean in general, e.g. for productive hosting?

[elmar-hinz]

@Joush: For me a typical scenario would be:

1. Current project
2. Quickfix of older project
3. OpenSource project: extension or core