Eng 4955 Procedure I/O statistics selectors

PROCEDUREINPUT and PROCEDUREOUTPUT are now @Statistics selectors, displaying timestamp, procedure, invocations, min/max/avg/tot and weighted percent of input/output. Both follow design of PROCEDUREPROFILE.

The code for StatsProcInputTable and StatsProcOutputTable is 90% similar, so it would make sense to make a superclass that can just pull stats specified in StatsAgent from the ProcedureStatsCollector