feat: activate rxnNotes field in Human-GEM

[haowang-bioinfo]

Main improvements in this PR:

• add rxnNotes field to Human-GEM, as planned in feat: add rxnNotes to Human-GEM  #272
• adjust importYaml/exportYaml functions to enable handling of rxnNotes field

I hereby confirm that I have:

• Tested my code on my own computer for running the model
• Passed testYamlConversion check
• Selected develop as a target branch

[mihai-sysbio]

Great! This will enable further cleanup of the references. Some additional questions:

• should this field be made visible on Metabolic Atlas?
• can the COBRA toolbox read this field from the yml file?

[haowang-bioinfo]

should this field be made visible on Metabolic Atlas?

This field is empty so far, so there is no point to make them visible now. Once they start to host useful information, then can be made visible IMO. A relevant question is "what information should be stored in this field?", which is added to #272.

can the COBRA toolbox read this field from the yml file?

Yes, COBRA toolbox supports this rxnNotes field.