Add Scale and Count aggregators.

The SCALE aggregator multiples all of its data points by a specified floating point value.  An example use case would be adjusting results of one query so that they display better alongside other queries.  (Sure, you can address this witj a separate Y Axis in the default UI, but that isn't the only UI out there.)

The COUNT aggregator simply counts the number of data points for the specified sampling interval. The target use case here is being able to count occurrences of some event by counting the number of data points which track some facet (say, duration) of that event.  In the absence of COUNT, you need to publish a second metric with a fixed value of one to enable the counting.