Turn off all write actions in production

We need to be able to deploy the bouncer app, which shares a database with this app. Currently this app can edit that database, but there aren't necessary safeguards to prevent misuse. Therefore we will temporarily disable editing from this app in production. Once we have implemented permissions and edit histories, we can remove the code in this PR.

Note that the implementation disables editing in preview too.

https://www.pivotaltracker.com/story/show/55153408