Flatten keywords in LegacyActor

[albireox]

Right now if the value of a keyword passed to LegacyActor.write is a dictionary, it's output as a dictionary even if that's incompatible with the legacy datamodel. For example

status = {
    "camera": {"name": camera.name, "uid": camera.uid},
    "status": camera.get_status(update=True),
}
command.info(status)

This will be output in a LegacyActor as 0 0 i camera={name: 'camera_name', uid: 'ML12345'}; status={temperature: 25.0}. Maybe this should just fail, but for now we can flatten it so that if a keyword is a dictionary with a single depth level, it gets converted into a list of values. The above would be

0 0 i camera=["camera_name", "ML12345"]; status=[25.0]