MAINT: migrate types/formats/transformers to q2-types for more general access

[gregcaporaso]

For example, see here.

[lizgehret]

Hey @hagenjp, I think this will be a good one for you to work on to familiarize yourself with the way that types/formats/transformers in the QIIME 2 ecosystem all work together. So, as a general jumping-off point on this one:

1. Check out the linked example @gregcaporaso provided above for the requested types that should be moved from q2-demux to q2-types.
   a. Make sure to check out how all of the semantic types are organized within q2-types. It may make sense to add these types under the per_sample_sequences dir (cc @gregcaporaso for any thoughts on that).
2. Take a look at the associated formats for these types under plugin_setup.py (all of the registered_semantic_type_to_format cases). All of the formats associated with the types above should also be migrated.
3. Take a look at all of the transformers that deal with the formats that are to be migrated - those should be moved as well.
4. Lastly, if there are any unit tests associated with the specific formats/transformers (hint: there are, and I will let you find those 🙂 ), those should be migrated as well.

When doing migrations like this, you'll want to open a PR that adds all of this functionality in the desired repo (in this case, that PR will be in q2-types), and then you'll want to open a second PR that removes this functionality from the original location (q2-demux).

Let me know if you have any questions; you can go ahead and start investigating this one when you're done with your open PRs!

[gregcaporaso]

@lizgehret, @hagenjp, multiplexed_sequences would be a better location for these, as these are not yet per-sample.

Thanks for writing up the roadmap for this one @lizgehret!