ArticlesController raises not_found RoutingError on article not found
Add valid_locales method to I18n
Add whit_locale method to I18n
Handle exceptions using exceptions_app middleware
Change locale expectation.

When locale is unknown it should raise a Routing error.
Set locale from request.

If locale is not coming in params[:locale] it'll be get from request.env['REQUEST_PATH']
Rename ExceptionsController to ErrorsController
ErrorsController render 404 and 500 errors pages.
Add localisation to error pages.
Revert "Add valid_locales method to I18n"

This reverts commit 92299b614454a838f6f203b4dd3fb16e33e5be85.

Conflicts:
	config/initializers/i18n/helpers.rb
	spec/config/initializers/i18n/helpers_spec.rb
Trim trailing white space on save
Switch to Gaffe for error handling

Must get better at Googling for gems :(

@pvcarrera
https://github.com/mirego/gaffe/
Merge branch 'error-handling'