[HttpKernel] Dependency management

This PR fixes an issue I'm having when trying to test a bundle without installing the whole framework. I just created a bundle and need to test whether it autoloads fine or not.

I need this piece of code to work : 

`use Symfony\Component\HttpKernel\Bundle\Bundle;`

Naturally, I install `symfony/http-kernel`, and then get the following error message : 

>  Class 'Symfony\Component\DependencyInjection\ContainerAware' not found in /home/users/gparis/dev/phpcasbundle/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/Bundle/Bundle.php

It seems there is a dependency between `http-kernel` and `dependency-injection`. This PR establishes this dependency. I'm not sure about the version constraint part though.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | [comma separated list of tickets fixed by the PR]
| License       | MIT