Allow setting a flag in custom_config.js to turn off the preliminary screen

Apologies for also squeezing in some formatting / 80col changes in here... the crux of the real changes are in `www/config.js` and `src/app.js`

I have set Blue to not have it.

Fixes #493
Merge pull request #494 from SpiderOak/issue-493-blue-should-not-have-the-preliminary-screen

Allow setting flag in custom config to turn off the preliminary screen