DOCS: outputs/postgresql improvements.
DOCS: outputs/postgresql improvements.

* Configuration parameters:
Linking the postgresql and psycopg documentation.
Completing the information with default values.

* Linking REQUIREMENTS.txt, removing one duplication of infos.

* Added FIXME for configuration unification with README.md.
Already removed some info that is in README.md.

aaronkaplan/intelmq,certtools/intelmq,certtools/intelmq,certtools/intelmq,aaronkaplan/intelmq,aaronkaplan/intelmq