Add more epitope databases to `datasets`

[grst]

List adapted from #54.

• [ ] The MAIT reference database with invariant CDR3
• [ ] huARdb https://academic.oup.com/nar/advance-article/doi/10.1093/nar/gkab857/6381136?rss=1
• [ ] McPAS-TCR
• [ ] PIRD
• [ ] The Adaptive Biotechnology database, used to identify (and exclude) public clonotypes shared between unrelated individuals (Dean et al., 2015)
• [ ] There might be quite some SARS-COV-2 TCR-epitope resources as well (e.g., Grifoni et al. 2021)
• [x] VDJDB
• [x] IEDB

[grst]

@ausserh, how about adding your code for IEDB to scirpy directly?

[grst]

More databases can potentially be accessed via biocypher. See also #404. CC @slobentanzer

[slobentanzer]

am on holiday, but will address this once i am back. mcpas is included in the adapters we did at the hackathon. cc @dbdimitrov