Local mode for easy dev / simple deployments

[guregu]

Let's add a flag that sets the server to "local mode" and instead of relying on Lambda / CF Workers to process/serve files, handles that stuff immediately.
I plan on adding this sometime this week, should help a lot.

[guregu]

Going to re-open this until someone else can get it running.
I've been removing stuff as I find it

[guregu]

FWIW I was able to successfully run it in a fresh shell with an empty environment, so I think the hard-coded stuff should be gone now. E-mail still needs to be made configurable but it's able to gracefully degrade (hide itself when disabled).

[guregu]

Confirmed working here #4 (comment)
Let's make separate issues for other things as we find them