[EPIC] Retinal Ganglion Cells editions

[aleixpuigb]

After the first session of the Human Retina Cell Atlas and RGC hackaton, there are some edits to implement into CL.

• Add taxon constraints to existing RGCs
• Add missing formal axioms based on text defs
  There are many cases with details of synaptic IO and morphology (mono vs bis-stratified) that are not reflected in formal axioms. A more complete representation might help with reconciliation.
• Add synonyms / merge based on the different nomenclatures
  Main focus = mouse where we have two nomenclatures + more in the literature.
• Add grouping orthology groups, starting with the classes that are populated (midget ON & OFF and parasol ON & OFF)

[dosumis]

Made some edits to list of tasks.