SQLite Support

We need to configure a few things to get everything working. As it stands, switching to SQLite 3 causes a few configuration options that default to calling `Rails.#{method}` to blow up.

See: https://github.com/rails/rails/blob/08754f12e65a9ec79633a605e986d0f1ffa4b251/activerecord/lib/active_record/tasks/database_tasks.rb#L27-L34

One thing that's missing: `DatabaseTasks.seed_loader` (an object that responds to `load_seed`). Without it, I don't think we have proper `db:seed` support (but I may be wrong).

This PR additionally changes the default from PostgreSQL to SQLite 3. I think it's the better default when you just want to hack on an idea. People'll switch to Postgres as soon as they need to, anyway.
Hmm. All of this should be happening in `lib/tasks/environment.rake`. Is that not loading correctly?