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.
Once we add spatial frequency (sf), we might have issues with this, because all image datasets will have a spatial frequency inherent feature, but mostly we just ignore that by having only a single size of DoG, which discards all but a narrow range of sf.  So the dataset will have sf inherently, but that won't be an error or even worthy of a warning. Hmm..