Change of PostgreSQL connector from psycopg2 to pg8000

[shovsj]

according to https://wiki.postgresql.org/wiki/Python,

Software	License	Platforms	Python versions	DB API 2.0	Native (uses libpq)	Last Release	Notes
Psycopg2	LGPL	Unix, Win32	2.6-3.6	yes	yes	2017	Most popular python driver, required for most Python+Postgres frameworks
pg8000	BSD	any (pure Python)	3.3+	yes	no	2019	Used by Web2Py. current updated official site
py-postgresql	BSD	any (pure Python)	3.0+	yes	no	2016	Pure Python with optional C accelerator modules,extensive custom API. Python 3 only.
PyGreSQL	BSD	Unix, Win32	2.6 thru 3.6	yes	yes	2017	The first PostgreSQL adapter for Python. Still actively maintained.
ocpgdb	BSD	Unix	2.3-2.6	yes	yes	2010	PG8.1+
bpgsql	LGPL	any (pure Python)	2.3-2.6	yes	no	2009	labeled alpha

We decide to change from psycopg2 to pg8000, to avoid a potential license issue

[shovsj]

This issue is closed by #464.