[Symfony] Command as service with constructor injection

[TomasVotruba]

Closes #19, resolves #20

Ref:

• https://matthiasnoback.nl/2013/10/symfony2-console-commands-as-services-why/
• https://stackoverflow.com/questions/7597912/how-can-i-inject-dependencies-to-symfony-console-commands/46013858#46013858
• https://stackoverflow.com/questions/19321760/symfony2-how-to-access-the-service-in-a-custom-console-command/46007150#46007150