[WIP] Imagick implementation

Refer to #34, I started a PR for Imagick implementation.

@Hast and @nick4fake, please tell me if you already start to work on it!

Here my TODO list:

 - [ ] Fill `Imagick` adapter class
 - [ ] If needed, adapt common adapter classes and GD
 - [ ] Write test for `Imagick` adapter class
 - [ ] Adapt test if common and/or GD classes are modified
 - [ ] Update documentation
 - [ ] Write an implementation on [ImageBundle](https://github.com/Gregwar/ImageBundle)

Please tell me if you think I missed some points on TODO list.

Some question for @Gregwar:
 - How do you use demo files?
 - How do you manage your test? How can I implement proper test for Imagick?
 - Imagick generaly throw errors when a function failed like [cropImage](http://php.net/manual/en/imagick.cropimage.php) for example. How should I manage it in adapter?

I will work on it some evenings and weekends, hope to finish that quickly.

Thanks.