Some improvements to Mixtures
- Added a model to misc called mixture_value that cause a phase that has this model to look into it's mixture object when updating it's value
- This used to be in the mixture_props file, but I generalized it and moved to misc, then deleted the mixture_props file
- This push BREAKS the saving of mixtures
A surprinzingly simple workaround (i.e. kludge) to fix the mixture problems
- The trouble was that during load, a phase object created and its models are added (which means they are all run by default to generate data)
- If data is needed from other objects that don't exist yet, then these models break
- I added a new 'regen_mode' to add_model called 'deferred' that adds the model to the _models dict, but doesn't run it
- The model does not need to be run since the data is added to the phase during the load.  It should already be in an up to date state
PNM.save/load now works with mixtures
- The root of all our problems is the object linking
- This means that objects must be re-initialized in the correct order and all kinds of tricks must be taken to recreate the linkages.
- There must be a better way!
- I'm hoping that the 'simulation controller' object will solve the problems, but this is a longer term aim now. I want to think about it and consider it carefully.