Add an ability to define aggregator_kwargs.

All the options are case insensitive now.
Example:
juggler:
    Aggregator: logic_or
    CRIT: ['${my_50x}/(${my_20x} > 0.1]
    Host: noxiouz.combaine
    Method: SMS
    checkname: http_err
    description: more that 10% of HTTP 50x errors!
    type: juggler
    aggregator_kwargs:
        ignore_nodata: 1