Introduce playtime
    
    playtime is a script aimed at allowing to trigger specific toddlers
    either manually or at certain times (if called via a cron).
    
    The toddlers will have to support this triggering mechanism.
    It however allows to leverage toddlers extensible structure to support
    time-triggered tasks in addition to message-bus-triggered ones.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>