Reduces data used in test to increase test speed
Relaxes ComplexCoverage param_dict requirement

If the parameteter_dictionary argument of the ComplexCoverage is None, a new empty ParameterDictionary is used and populated with the parameters from all referenced coverages
Simplifies _dobuild signature
Fixes sparse value bug; adds ComplexCoverage test

Fixes bug when slicing against a SparseConstantValue that is utilizing AbstractParameterValue classes under the hood (as is the case with ComplexCoverage)

Adds test_temporal_aggregation_all_param_types test - to ensure temporal aggregation works with all parameter types
Adds ComplexCoverage.append_reference_coverage()

Adds function 'append_reference_coverage' to ComplexCoverage to allow additional coverages to be added to the ComplexCoverage post-creation.  Ordering of the reference coverages is maintained.

Also adds test_append_reference_coverage
Restricts parameters stored in ComplexCoverage

Only allows storage of ParameterFunctionType parameters within ComplexCoverage