MOD: more general way to parse metric specific thread data
ADD: added new class dict and method _agg_indices  & define_agg_indices() to handle which indices aggregators operate on
ADD: _data_model_definition class dict to all metric classes.  Preprocessing method for metric class init.
RM: field indices list from `aggregator()` args
FIX: moved call to class preprocessing method outside of class scope
ADD: functionality for generating time-series data.