uc service logs or uc logs — view service logs similar to docker logs.

As the first iteration, we can show only logs for active containers but ideally we'd like to preserve all logs for a service, including from the stopped and removed containers (replaced by new deploys).

Figure out if we need to implement own logs aggregator on each host with rotated storage and configure it as the default instead of the currently configured local driver: #83. IIUC Flynn had something similar: https://github.com/flynn/flynn/blob/master/docs/content/production.html.md#retrieving-logs