Better error message for Mindtagger PORT collision

Fixes #1
Mindtagger: fixed TSV and Postgres array parsing

Postgres arrays serialized in CSV were being parsed incorrectly, because
TSV escapes were being incorrectly handled while parsing Postgres
arrays.  Now, TSVs escapes are handled earlier at the backend, so the
frontend receives the same data regardless of the items input format:
CSV or TSV.

Fixes HazyResearch/deepdive#173