* refactor and improve successful origin

* use appropriate origin for creating referendum

* fmt

* add setup tally feature for benchmarks

* feedback updates

* fmt

* Update frame/referenda/src/benchmarking.rs

Co-authored-by: Gavin Wood <gavin@parity.io>

* feedback on `setup` trait

* fix

Co-authored-by: Gavin Wood <gavin@parity.io>