Improve some minor things

No super big changes, but I wanted to put in a bit of work today. Can someone give this a look over and merge it if it makes sense?

Key points:
1) minor visual improvements to the mayor candidate boxes on the homepage
2) using foreman (with a `.env` file) to set DATABASE_URL instead of expecting people to do it themselves
3) adding a bright disclaimer to the top of every page, so people don't accidentally come to the conclusion that we know what we're doing (...yet :wink:)