Further abstraction in ModelMethod

[JosePizarro3]

Here you have the changes. I took the opportunity and added model_method_ref to Outputs as well.

I think one reviewer is enough, but if any of you want (@ndaelman-hu @Bernadette-Mohr) let me know and I add you as reviewers.

Closes #92

[coveralls]

Pull Request Test Coverage Report for Build 9694408630

Details

• 16 of 17 (94.12%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.2%) to 79.273%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/nomad_simulations/schema_packages/model_method.py	6	7	85.71%

Files with Coverage Reduction	New Missed Lines	%
src/nomad_simulations/schema_packages/model_method.py	3	70.94%

Totals
Change from base Build 9663609101:	0.2%
Covered Lines:	1549
Relevant Lines:	1954

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9694436071

Details

• 18 of 19 (94.74%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 79.273%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/nomad_simulations/schema_packages/model_method.py	8	9	88.89%

Totals
Change from base Build 9663609101:	0.2%
Covered Lines:	1549
Relevant Lines:	1954

---

💛 - Coveralls

[JFRudzinski]

structure makes sense to me, fits perfectly with what I started creating for FFs before 👍

Just the one small question about the definition of parameters in general