Custom categorical overlays

[d-callan]

ive assumed that overlay values are required for high cardinality categorical or continuous overlays. ive also assumed that continuous overlay values will be handled in a separate pr and that the overlay values present are from the vocabulary (meaning if i get a value like 'Other' it means i should look for that as a real value).

for categorical overlays, all values which arent among those specified by the user become 'All un-selected values', but that can be changed if needed.

[d-callan]

resolves #205

[d-callan]

@bobular id appreciate your thoughts prior to my writing documentation and updating tests, in case we decide to change something

[d-callan]

worth noting this is going to change the behavior of the eda map viz too, which i think is ok bc in a recent ux call we agreed to set the map viz constraints in the same way we do other eda vizs

[bobular]

Hi @d-callan - thanks for reminding me about the regular EDA map viz. The back end will no longer do 7+Other by default for high cardinality categoricals. At a minimum (to maintain status quo) the client will need to request the "value metadata" (values and their counts) and then send the top 7 with the map-markers-overlay request. At a maximum we'd provide some "paint by variable config" like in the standalone map. Am I getting this right?

[d-callan]

there was a ux meeting where people said theyd be ok to just say you can only use variables w 8 or fewer values in the map, like the other vizs, and figure out high cardinality vars etc more generally at a later date. i suspect that will mean allowing some amount of user configuration for them at some point yes, but the backend is now in a better position to support that as well.