https://codereview.appspot.com/318800043/

The statistics module enhancements can be summarized as follows: 
 - Modified gnuplot-aggregator
 - Moved application-packet-probe to stats from applications module
 - A set of (example) helper classes for setting up the delay and throughput statistics
 - A stats-helper-example illustrating the usage of the additions
 - A test suite for distribution collectors
 - Sphinx documentation (.rst files) has been updated related to the additions
 - A set of new probes, collectors and aggragators listed below 

New probes:
 - bytes-probe
 - application packet probe 

New collectors
 - collector-map
 - distribution-collector
 - interval-rate-collector
 - scalar-collector
 - unit-conversion-collector 

New aggregators:
 - multi-file-aggregator

 Other
 - traffic-time-tag
 - stats-callback-definitions