Version 2

**Changes:**
* change the way filters are applied, we now trigger an event with a custom name for each filter type instead of a global event with a listener for each filter.
* allow to defined listener for specific form type field.
* Transformer are replaced by DataExtractor.
* added FilterOperands class to regroup all constants filter types.
* the bundle now support Doctrine ORM and DBAL 
* by default we register listeners for filter_xxx types provided by the bundle and also for some form types from SF.
* replace AbstractFilterType by FilterTypeExtension to be able to use apply_filter option with all form types

**Todo before mergin this PR:**
- [x] rewrite/improve the documentation.
- [x] create a new branch from master to provide support for current version after merge.
- [x] check compatibility wtih sf2.3