mpmetrics.register(properties, type, days);

Required:
@properties: A dictionary of properties in the usual format. {"key" : "value", "key2", "value2"}

Optional:
@type: The type of event to register these properties for
    "all": All data (DEFAULT)
    "events": Only events
    "funnels": Only funnels
@days: The number of days to store this information (DEFAULT 7)