keep species_id as an array in the distinct observations rather than code

[smnorris]

Species codes are easier to work with than ids, but by storing the ids in the array we can use https://www.postgresql.org/docs/12/intarray.html for indexed (instant) searches - I think this is worth the tradeoff.

[smnorris]

Turns out the species_codes array is super useful for map labels. Keep species_ids but add species_codes back into output tables/views.