unify capitalization of variables and parameters

[fbenke-pik]

Purpose of this PR

Unifies capitalization of variables an parameters so that REMIND passes soon-to-be introduced codeCheck

Whenever possible, the code uses the capitalization as declared in declarations.gms and sets.gms.

Type of change

• Refactoring

Checklist:

• My code follows the coding etiquette
• I performed a self-review of my own code
• I explained my changes within the PR, particularly in hard-to-understand areas
• I checked that the in-code documentation is up-to-date
• I adjusted the reporting in remind2 where it was needed
• All automated model tests pass (FAIL 0 in the output of make test)

[LaviniaBaumstark]

did you also check the scripts part of teh GAMS repo and that the reporting is still working?

[0UmfHxcvx5J7JoaOhFSs5mncnisTJJ6q]

… adding insult to injury asking me to approve this.

[fbenke-pik]

Nah, I added you to give you the chance to raise concerns / stop this before this is merged (also, because it affects the industry module a lot).