Tech debt: refactor sql_utils to better seperate codeableconcepts and codings

[dogversioning]

The logic for handling both of these goes through some of the same infrastructure in a way that suggests they are interchangable, and they really aren't - it should be clearer which bits are intentionally shared, and which bits aren't, and the number of public interfaces in the file should be trimmed down to be solely based on class inputs.

[dogversioning]

#196 gets started on this.