MAINT: refactor/clean up GenomeData types

[misialq]

This PRs refactors some of the GenomeData types and introduces new types which will be required in q2-moshpit. Below is the summary of the changes:

• removed SampleData[BLAST6] type - this was used to store orthologs detected by EggNOG but will be replaced by SampleData[Orthologs] (see below)
• introduced SampleData[Orthologs] and GenomeData[Orthologs] to store the orthologs produced by EggNOG+Diamond; the BLAST6 variant was not really the best choice as the table produced by EggNOG bears only a degree of similarity to a "proper" BLAST6 result table; using the separate type for those orthologs will allow us to be more explicit and clear about the contents (the type actually already existed but we did not use it)
• removed OG and KEGG types - we are not using those anywhere and will not; they had been designed in the beginning of the project, before we knew exactly what outputs from functional annotation we would want to store and how
• introduced GenomeData[DNASequence] to represent collections of genome sequences fetched from various sources; we want to be able to store each genome in a separate file so the FeatureData[Sequence] was not a good candidate

[misialq]

Hey @lizgehret, do you think you could look this over? I think I'll still need to add some tests for the new type introduced here but the rest of the code should be ready.

Just FYI, @nbokulich - these are changes we talked about today, in case you want to check those out.

[misialq]

Hey @lizgehret, I'm done with the changes here - I added one test for the new directory format and refactored some paths to test files for consistency.

[misialq]

Hmmm this is very weird - some tests are failing due to some directories supposedly not being there. I looked through setup.py and the tests themselves but cannot really see what the problem is. They also pass locally for me. Do you spot what's wrong @lizgehret? 👀

[lizgehret]

i think i found the issue(s) @misialq - letting the tests run now to confirm!

[misialq]

Aaaaaaah, all these commas 🤦 Thanks for fixing! Feel free to merge any time 🚀