DocumentController specs passing

* New class Settings adds default settings e.g. for test environment
Fix up DB config for Travis
Bash script to tide me over until this thing is usable
Set up the *test* database for Travis
Fix?
Try to get the database to persist
And again
And again...
Switch to PostGres so that the database will persist properly.

Hopefully this gets the test working correctly, cos an in-memory SQLite
database wasn't cutting the mustard.
Move Travis DB config to database.travis.yml
Dev hack to make `Scanner#scan` work sans hardware
Use AppConfiguration instead of rolling my own
Configure a directory to put documents in
Fix crash on start when `tmp/` doesn't exist
Make lots of changes, like adding UserController
Add Dropbox access token to User model
Upload documents to Dropbox
Make saving to Dropbox optional
Fix tests
Eliminate pending tests