Refactor in memory test persistence

To a more realistic state before switching to postgres
Set up Postgres persistence with sequel gem

Helper scripts for:
* Create database
* Generate migration
* Run migrations

+ @kalleth

Sequel gem
Working Postgres integration with HStore

+ @kalleth
Extract mapper from repository

Mapper is trivial at this point but the presence
of this seam should keep the two concerns separate.
Move load paths and constants to config/env
Move config into YAML files

Load the config by merging together YAML files in the config directory instead
of having a bunch of constants lying around.

Pass the single config hash into the `Application` on initialization.

Also remove all default parameters from `Application` so that it's used in the
same way in test and production.

Conflicts:
	application.rb
	features/support/env.rb
Perform database setup for CI

Provide a separate config used for the app in CI. Alter jenkins script
to run migrations and run rake task to create databases and add
extensions.
Fix migration scripts to work with new config scheme
Merge pull request #7 from alphagov/persistence

Persistence