Add computed columns to soda fountain upsert flow

- Factored out RowDataTranslator from RowDAO and separated out client JSON -> SoQLValue and SoQLValue -> DC JSON
- Computed columns field name must start with colon, this ensures they are treated like system columns in select statements (returned in SELECT :* but not SELECT *). There were a bunch of ways we could have implemented this but based on talks with Marc, Robert, Franklin this had the best tradeoffs for now.
- Tightened up some of the column validations in Soda Fountain (a) Currently 2 columns are allowed to have the same field_name, which creates ambiguity in SoQL SELECT statements. (b) Don't allow client to specify computed column values in an upsert/replace
Hey, I think it's fine to return, it _should_ work but is a bit unintuitive.

`takeWhile` doesn't fix anything but I think it reads better.  It implies that we terminate the stream upon a certain condition, whereas `collect` implies the entire stream is filtered.