Revamp README to bring up to date in terms of status and make a large nu...

...mber of small improvements to the redeployer-oriented documentation

This PR's changes include:

- Remove outdated notice of project status
- Add screenshot and better flushing out of the steps needed to use CityVoice yourself
- Add the step in deployment for adding your custom files
- Move optional features / config to a standalone doc file
- Add details for the needing the Heroku toolbelt to deploy
- Clarify in the section header that local installation is for developers
- Various improvements to making_a_survey.md for usability

Many thanks to @cydharrell and @criscristina for the great feedback that informed these improvements.