Update error handling

[aidanbh]

• Move error message responsibility from JSscout to GoScout
• JScout clears on HTTP codes < 300 and 409
• GoScout returns 201 for creating new record, 409 for rejected duplicate (w/ error explanation in response), and 500 for other SQL errors (w/ SQL error code+text in response if decode-able)

rn the 201 text shows up as garbled (FF) or blank (Edge, Safari) so that needs to be fixed. Tried with response writer and http.Error(). Could hardcore in interim but if it doesn't even show up on mobile this isn't a blocking issue.

[aidanbh]

Manual testing complete in test server, merging