Started to integrate propel [WIP]
Use the PropertyAccess component to manipulate objects
Cleaned a bit the configuration definition
Fixed dependency constraint
Fixed a few typos
Added a few tests for the PropelAdapter class
Updated FileInjectorTest
Updated PropertyMapping tests
Updated DoctrineUploaderListener tests
Updated Tests/Storage/FileSystemStorageTest.php
Fixed GaufretteStorage test
Little cs fix
Renamed MappingReader to MetadataReader
Cleaned adapters definition
Fixed a few typos
Moar cs fixes
Added a few tests for the PropelUploader listener
Fixed doctrine related listeners
Updated propel event dispatcher dependency dependency
Reduced the coupling with reflection objects

For now, the main benefit is that Doctrine/Propel entities are no longer
required to generate file links (with Twig `vich_uploader_asset`
function for instance).

The following becomes possible:

```html+jinja
{{ vich_uploader_asset(entry, 'imageFile', 'FooBundle\Entity\Entry') }}
```

Where `entry` isn't an object but an array.

This would close the issue #138