[WIP] Missing comments in ISA-JSON/ISA-TAB

[Zigur]

The following ISA-API objects are Commentable:

• Investigation
• OntologySource
• OntologyAnnotation
• Publication
• Person
• Study
• StudyFactor
• Assay
• Protocol
• ProtocolParameter
• ParameterValue
• ProtocolComponent
• Source
• Characteristic
• Sample
• Material
• FactorValue
• Process
• DataFile

This PR aims to:

• add the "comments" to the JSON schemas referring to all the objects above.
• serialise comments for all the objects/classes above in ISA-JSON
• deserialise comments for all the objects/classes above in ISA-JSON
• serialise and deserialise comments for all the objects/classes above in ISA-TAB.

[coveralls]

Coverage increased (+0.4%) to 75.734% when pulling 36be6d1 on bugfix/comments into 9b1feb8 on master.

[Zigur]

With commit ca8b1d0, in isajson.load there fields load comments

• Investigation
• OntologySource
• OntologyAnnotation:
  • as characteristic categories in Assays
  • as characteristic categories in Studies
  • measure units
  • Publication status
  • Design descriptors
  • Protocol types
  • Parameter Names
  • Component types
  • Characteristic values in sources
  • Characteristic values in samples
  • FactorValue "values"
  • Assay units
  • assay characteristic categories
  • characteristic values in other materials
• Publication
• Person
  • study person
• Study
• StudyFactor
• Assay
• [ ]Protocol
• ProtocolParameter
• ParameterValue
  • Parameter values in studies
  • Parameter values in assays
• ProtocolComponent
• Source
• Characteristic
  • characteristics in sources
  • characteristics in samples
  • characteristics in other materials
• Sample
• Material
  • "other" material in assays
• FactorValue
  • factor values in samples
• Process
  • processes in studies
  • processes in assays
• DataFile

[proccaserra]

@Zigur looks good for me for all the ISA-JSON serialization and most of ISA-Tab serialization.
For the ISA-Tab serialization, I have spotted a minor issue, i.e. failure to serialize Comments on ISA.OntologyAnnotation object if/when used on ISA.FactorType and ISA.Protocol.ParameterName (which is treated like an Ontology Term).

I have documented this in a jupyter notebook.