Actions CLI - tracer implementation

Just connects the command line 'actions' and 'do' to the apiserver; basic initial CLI implementation
I'm not sure this definitely is a unit name, is it? I'd naively expect either `juju actions` or `juju action list` (or however we spell it) to tell me something (probably something quite compact) about all the (active or recently completed?) actions in my environment; and to have various flags for refining the result. --unit, --service, --status, etc? --name (of the action?)