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.
I hate to just keep changing names, but it looks like generator_name should be pattern_name, if it's in a list that includes pattern and pattern_number.  Or maybe pattern_label is better, so that it's clear that it's not the name of the class, but a label applied by the user.  Your choice!