Update documentation based on changes that came from the epitopeprediction subworkflow integration and the protein input path

[xXFloBaerXx]

• Update metapep_datamodel.png (Rank score should be there, but quantities in relations and [pk] deletion needs to be checked). Datamodel should be fine now (Add Protein Input Path #179), just the SVG and the PNG needs to be regenerated.
• show_supported_models.py needs to have right tool versions (maybe not hardcoded) and correct peptide ranges
• nextflow.config: File external_tools_meta.json is not existing
• usage.md: wrong pipeline in bash example
• CITATIONS.md: Citation of epitopeprediction pipeline
• prepare_entity_binding_ratios.py: Mention also NetMHCpan in comments
• Add PR links to changelog until release