Use symfony/console for new CLI commands

- Require symfony/console package via Composer.
- Include PSR-4 autoloading for commands in application/Command.
- Add an example command from Symfony tutorial.
- Add an executable `console` file to trigger the Console Application.
- Both Composer and Kohana autoloading is available in console commands.
- Minion tasks are still runnable.
Merge pull request #2 from Despark/symfony-console

Use symfony/console for new CLI commands