Implemented alternative methods to describe mappings.

For now, only Annotations and Yaml are supported. XML will come later.
Merge pull request #159 from K-Phoen/dev-mapping

Support alternative mapping formats
fix exception namespace

PHP Fatal error:  Class 'Vich\UploaderBundle\DependencyInjection\RuntimeException' not found in ...\vendor\vich\uploader-bundle\Vich\UploaderBundle\DependencyInjection\VichUploaderExtension.php on line 145
Merge pull request #173 from Gemorroj/patch-1

Fix exception namespace