Large update for the SumStats framework.

- On-demand access to sumstats results through "return from"
   functions named SumStats::request and Sumstats::request_key.
   Both functions are tested in standalone and clustered modes.

 - $name field has returned to SumStats which simplifies cluster
   code and makes the on-demand access stuff possible.

 - Clustered results can only be collected for 1 minute from their
   time of creation now instead of time of last read.

 - Thresholds use doubles instead of counts everywhere now.

 - Calculation dependency resolution occurs at start up time now
   instead of doing it at observation time which provide a minor
   cpu performance improvement.  A new plugin registration mechanism
   was created to support this change.

 - AppStats now has a minimal doc string and is broken into hook-based
   plugins.

 - AppStats and traceroute detection added to local.bro

testing/btest/scripts/base/frameworks/sumstats/basic-cluster.bro

@@ -23,7 +23,8 @@ global n = 0;
 event bro_init() &priority=5
 	{
 	local r1: SumStats::Reducer = [$stream="test", $apply=set(SumStats::SUM, SumStats::MIN, SumStats::MAX, SumStats::AVERAGE, SumStats::STD_DEV, SumStats::VARIANCE, SumStats::UNIQUE)];
-	SumStats::create([$epoch=5secs,
+	SumStats::create([$name="test",
+	                  $epoch=5secs,
 	                  $reducers=set(r1),
 	                  $epoch_finished(rt: SumStats::ResultTable) =
 	                  	{