Map: plan where and how to handle multi-valued variables in back end

[bobular]

Related to VEuPathDB/EdaNewIssues#635

Some popbio variables are importantly multi-valued:

• collection.attractant
• method/protocol variables for collection and assay entities

Multi-valued variables cause all sorts of problems (mainly with entity counting) and I'm not saying we should handle them everywhere. Being able to filter them is a must, and we already have this. It would be nice to solve this issue for map-markers (because it's a fairly informal visualization) if we can. Maybe less so the others.

Currently collection.device is multi-valued and we are debating if that's a curation issue.

[d-callan]

I dont think this is a req for an initial release of the map right? Im thinking to move it to the other board.