Added PatternCoordinator class which returns a set of coordinated pattern generators

A PatternCoordinator is a set of coordinated pattern generators.
The pattern generators are named according to the labels parameter.
The dimensions to be returned are specified with the dims parameter.
PatternGenerators are first instantiated with the parameters specified in input_parameters, and then subclasses of ValueCoordinator are applied to modify the properties of these generators.
And here maybe inputs_per_generator would be num_patterns_per_label, or maybe patterns_per_label?  Definitely something with "pattern" rather than inputs, as this file is all about patterns, not inputs or generators.