created $ignore_time options for track_charge() and unset() methods

[gelzis]

example using unset()

    Mixpanel.people.unset(mixPanelID, {
        properties : ['Downgraded', 'Unsuccessful charges'],
        settings : {'$ignore_time' : true}
    }, cb);

example using track_charge()

Mixpanel.people.track_charge(mixPanelID, 18, {'$ignore_time' : true}, cb);

[emgeee]

+1