Add parametrisation examples

[ikorotkin]

Added 5 parametrisation examples:

• nmc_pouch_cell_BPX.json from About:Energy open-source release (DFN parametrisation)
• lfp_18650_cell_BPX.json from About:Energy open-source release (DFN parametrisation)
• Example of blended electrode definition with two particle sizes but equivalent chemistry
• Example of user-defined 0th-order hysteresis for graphite-Si blend in negative electrode
• SPM parametrisation example based on nmc_pouch_cell_BPX.json

From the email chain:

• [ ] For blended electrodes and SPM(e): define the equations that are expected to be obeyed, see issue #29
• [ ] Should we be more strict in how the phases are labelled (e.g., make them "Primary", "Secondary")?

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[ejfdickinson]

@ikorotkin @rtimms

I disagree with the suggestion to restrict what BPX users can call the components of a blended electrode for the following reasons:

• Free naming supports a human-readable standard. People may use the functionality for different reasons – different chemistries, different particle sizes, or as ways to implement more complex models in conjunction with user-defined parameters.
• “Primary” and “secondary” particle have a specific physical meaning in the sense of an agglomerate (in which they actually refer to the same material, but grouped at different scales). Locking that specific nomenclature would be locking something ambiguous / wrong.
• It doesn't solve the problem of inequivalent BPX files encoding the same model, because you can always permute the parallel electrode contributions. We would want a more general comparison / diff tool for BPX, as well as perhaps a tool to reduce a BPX file to a "canonical" limiting reporting standard, in which user-specific naming could be stripped.