Cheek Samples

[cassidysymons]

This PR is intended to address the needs surrounding collecting skin samples from cheeks:

1. It adds Cheek as a valid sample site and adds applicable constants to the metadata pulldown process.

2. It adds the notion of "barcode metadata," which are fields that are strictly linked to samples, rather than implicitly linked to samples via sources (as all of the existing survey questions are).

From a UX perspective, the reason for this deviation is the temporal importance of the questions. While all metadata are temporally linked to samples, and we strive to close that gap as much as possible, these particular questions are directly related to preparation for the sample collection.

From a technical perspective, I opted to establish a new avenue of storage because neither existing method felt appropriate:

• Utilizing the survey framework would be excessively heavy and would require a significant amount of hacking up code to expose three questions to the user interface.
• Storing the data in the ag_kit_barcodes table would be far less than ideal given that they only apply to a small fraction of samples.

The middle ground I established is sufficient for the purpose - including data validation - and could be extended into a more robust framework if future use calls for it.

Corresponding microsetta-interface PR is biocore/microsetta-interface#334

[AmandaBirmingham]

One question/future request re constant metadata values for cheek samples.