Fully separate concerns between Scenario and Runner

WIP
* [x] Runner should take a pre-built Scenario
* [ ] Scenario #compile should be the point at which a path is taken
* [ ] Default to using temporary files for generated scenarios unless they are explicitly compiled to disk
* [ ] Overhaul CLI - Replace -c and -r options on CLI with full commands, ie sippy_cup run foo_scenario, sippy_cup compile foo_scenario