Include postgres MIMIC-III concepts

[alistairewj]

There were a few scripts that weren't working in the MIMIC-III folder. This PR:

1. Adds a shell script which converts BigQuery syntax to PostgreSQL syntax, and outputs a postgres-make-concepts.sql script (this is the approach taken by MIMIC-IV)
2. Adds the postgres concepts to the repo (some of them are not automatically generated, which fixes bugs which have been raised to me outside this repo)
3. Fixes other misc bugs with the concept scripts I found

I tested the postgres-make-concepts.sql script and all the concepts build in postgres v14.