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 guess that's how it has to be, though perhaps there is something we could do in the definition of ClassSelector, particularly to allow the correct inheritance of is_instance.  I've no idea, but meanwhile at least you have something that works properly now.

-- 
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.