ENH: General refactor todos

[nury12n]

This will be likely be a running list of things to re-factor over time.

• Lean more into dependency injection. Some modules are sort of doing this already, but we should be more explicit
• Clarity on some of the different functions in GenericModel. There's some functions that need to be implemented while other functions are optional and can be overridden. Other functions can be overridden but has underlying functionality that needs to be called through super(). (see open/close principle)
  • There's probably other objects to do this on as well
• Refactor documentation. We should group it into precipitation, diffusion, thermodynamics, etc. This should be done with the mobility fitting branch Mobility fitting #19 since we started doing this in the examples.
• Generalize the model data. See ENH: Saving/loading model parameters #20
  • One thing here would also be to move the strength model data into the precipitate model so we don't have two data objects to save/load