inveniomanage: demosite create/populate/drop
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 <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

tiborsimko/invenio-formatter,inveniosoftware/invenio-formatter,tiborsimko/invenio-formatter,inveniosoftware/invenio-formatter,tiborsimko/invenio-formatter,inveniosoftware/invenio-formatter