Inject $app into controller constructor

I've recently been using controllers as services and ran into a bit of an issue with not being able to the $app from within. Below is the documented way of doing this:

``` php
public function action (Application $app) {
    // acton code
}
```

This works great until I want to extend from a base controller. I use this for various helper commands for rending twig templates or ouputting/logging errors from within the application. The only way I can see how to do this is like below:

``` php
public function action1 (Application $app) {
    $this->app = $app;
    // rest of action code
}
// ... more actions in controller, each needing that top line
```

To avoid having to do this in every action, as there may be many I added this snippet which is taken from the symfony http-kernel component. It basically just passes $app to the constructor, then the base controller can set ```$this->app``` from it's constructor for all of the actions (and base helper functions) to access.

Apologies if I've overlooked a better way of doing this.

Thanks
/Marc