inveniomanage: demosite create/populate/drop
- Moves commands from database_manager to demosite_manager. (closes #1534)
- Introduces scriptutils for various decorators and Manager modifications.
- Improves change_command_name decorator for replacing '_' by '-' or setting up desired command name.
Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>