DWI derivatives: Compulsory "parameter" entity

[Lestropie]

Realised this discrepancy while using the demonstrative examples for another purpose. Would like to make a reasonable decision on this prior to the data being presented elsewhere.

Will need to be resolved against #51.

[arokem]

With #51 merged, I think all mentions of parameter here should be changed to param.

Remind me again why tensor components need the all modifier?

[Lestropie]

Remind me again why tensor components need the all modifier?

By making "_param-all" compulsory for any model where all components are encased within a single file, it makes validation far easier. This makes more sense on the premise that #46 is merged. Any file with suffix "model" would always necessitate the definition of entities "model" and "param". If such models are allowed to omit the "param" entity, then the validator (and potentially software reading from such data that attempts to be somewhat model-agnostic) would need to be able to look at other contents in the directory to make sure that there are no other files belonging to the same model.

Happy to have that debate, I certainly had it internally, but it warrants its own issue listing in that case.