Add `quick-start.sh` to backdrop root

- I got quite tired of the `./start-app` way of life, passing two arguments to the same script twice.
- Starts both read and write on the expected ports (3038/3039), and takes no arguments
- This is an alternative to bowl-ing the app, for clods like me who can't think outside of the repository the app sits in.
run_development to match stagecraft convention
Merge pull request #295 from alphagov/quickstart

Add `quick-start.sh` to backdrop root