NIO-1125, adding block messages

[f1401martin]

@mattdodge I changed the implementation to match the results you expected in the first place

{
    "status": "started, warning",
    "pid": 98403,
    "parent_pid": 98397,
    "full_status": {
        "service": "started",
        "blocks": {
            "my_logger": {
                "status": "started"
            },
            "my_sub": {
                "status": "started, warning",
                "warning": "Block is not connected"
            },
            "my_pub": {
                "status": "started, warning",
                "warning": "Block is not connected"
            },
            "ee49544c-cdf7-48ad-9780-2ae9653c8d23": {
                "status": "started"
            }
        }
    }
}

the only thing I find with this approach is that calling API would have to "parse" to find out if a message is returned, is that too weird? (Note: I have a different branch with a different implementation, it is more elaborate and returns a more verbose result...)