IMP: transformers SingleLanePerSample... to Casava

[thermokarst]

Fixes #209

Related to qiime2/q2-quality-control#52

---

Missing unit tests

[thermokarst]

Relevant discussion here: qiime2/q2-quality-control#52

I'm not sure yet about the transformer here

https://github.com/qiime2/q2-types/pull/245/files#diff-3fd5d1462a2b3d80c0d3c98949f10949R94-R102

The problem is that it ends up producing a useless basepath, which ultimately needs to be rewritten in the format property. Perhaps it would be better to eliminate that transformer altogether and stick it all in the property, I was just trying to recycle as much of the transformers functionality as I possibly could. Open to ideas.

[thermokarst]

I'm not sure yet about the transformer here

The more I think about this, the more I want to refactor as internal utils used by the fmt property && the transformers, and dropping this transformer.

[thermokarst]

Okay, the diff is pretty gross because there is a bit of code churn, but the refactor looks like this: first I moved all the utils out of _transformer.py and into a new shared _util.py. The new util module is used by the transformers module && the formats module, so I had to refactor the utils so that they injected their format dependencies at runtime (I am open to other suggestions, just let me know). Then I created some new dynamic utils via functool, to cut down on the boilerplate. Lastly, I refactored the dynamic manifest property on the format to use the shared utils.

[thermokarst]

BTW - this is still missing unit tests, but I can add those as part of my response-to-review.

[nbokulich]

Thanks @thermokarst ! This LGTM, I just have one inline comment.