Add airbrake

Airbrake is being used to track our errors through errbit. The
initializer is overridden on deployment.
If request is invalid respond with unprocessable
Merge pull request #8 from alphagov/feature/unprocessible-requests

If the request is invalid respond with unprocessable
Fix unprocess[ia]ble typo
Merge pull request #6 from alphagov/airbrake

Add airbrake
Merge pull request #9 from alphagov/fix-unprocessible-typo

Fix unprocess[ia]ble typo
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
Hack to make postgres HSTORE store array values
Make #find_by_tags actually return the objects
Merge pull request #10 from alphagov/hstore-hack

Hack to make postgres HSTORE store array values
Domain layer helpers for Cucumber
Notifications by tag wired up

Yet to test / implement
* Real tag searching
* GovDelivery API support