- Refactoring index action: retrieving data was moved to the model
- Implemented support for job advertisments expiration (app.yml)
- Added grouping job advertisments by categories,
  added limiting list on the homepage (app.yml)
- Updated fixture by adding 30 generated job advertisments
  just for tests
- Update according to
  `Day 6: More with the Model` available at:
  http://symfony.com/legacy/doc/jobeet/1_4/en/06?orm=Doctrine