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.
inherent_dims [now inherent_features?] can be used to declare that for the dataset in use, the specified features are inherently forced to vary and need not be synthesized using the metafeature_mapping [now feature_coordinators].