Add empty collection filter

New filter for doctrine, empty collection. When you make a copy of your object, matched element with this filter will be reset as an empty array collection. 

He is very ligh and usefull. 

NOTICE : I have rename the test class of DoctrineCollection accoding to the class name under test. (But i changed nothing)
Yep sorry, phpstorm add it automatically and I have not noticed. I clean it.