[Uploadable] uploadable object as third parameter added to FilenameGeneratorInterface

By this change now in our custom FilenameGenerator class we can use uploadable object fields.
For example if you want SEO friendly filename, now you can use object's slug field for filename generation...

Actually this is PR for Issue #440.
This simple and very useful solution is from @patie:
https://github.com/patie/DoctrineExtensions/commits/master.