Slow mode money limit

Change the slow mode from a QPS hard coded limit to a authorized money limit that is settable as an option in the launch script.

I tested it through forcing slow mode and looking at the cummulatedBidPrice. 
Here the first test was with 100 CPM as limit, though that is too low to bid, then with 1000, next 2000, 5000 and finally without a limit.
You can see it does what is expected.

![testing_slow_mode](https://cloud.githubusercontent.com/assets/2280752/4208018/59d4d360-385c-11e4-9255-c5cf93635f88.png)

I could do a sendBidDroppedMessage, maybe this is more appropriate message? 

I'm not sure I agree with letting those bids through though, because depending on the throughput of the bids that means the spending will be very variable, from second to second. So In order to make it a hard limit it's better to drop those bids.

I do know that dropping the bids will incur a processing loss, however, from what I understand slow mode is a safety measure, if I assume it doesn't run very often then it's not that much of a processing waste.