installation: demosite fixtures addition
- Introduces new command inveniomanage database demosite to populate demosite from fixtures.
- NOTE inveiniocfg --create-demo-site is still using sql data for testing purposes.
- DEPRECATED democfgdata.sql in flavor of *_fixtures_demosite.py
Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>