Allow to configure Sluggable managed filters

This change allows to configure managed filters in Sluggable listener.

This is useful in case you are having issues with using Sluggable + Softdeleteable + Unique ( l3pp4rd/DoctrineExtensions#449 ).

Implementation suggested by @l3pp4rd in https://github.com/l3pp4rd/DoctrineExtensions/pull/549

This is PR https://github.com/stof/StofDoctrineExtensionsBundle/issues/185 by @stanislavprokopov reopened because of previous close. It is useful and should be merged into bundle.