Added sonata_type_model_autocomplete form type

Added support for many-to-many in sonata_type_model_autocomplete

Changed `collection` form type to `sonata_type_native_collection`

Fixed unit tests

Fixed issues with Sf 2.3

Fixed dates in changelog

Fixed minor issues

Make code more universal.

Another improvements. Fixed bugs in paging.

Added toStringCallback option. Fixed datagrid parameters.

Fixed unit tests

Improved code coverage of Datagrid

Improved doc and added some more tests

Fixed CS

Conflicts:
	CHANGELOG.md
	Controller/HelperController.php
	Datagrid/Datagrid.php
	Form/DataTransformer/ModelToIdPropertyTransformer.php
	Form/Type/ModelAutocompleteType.php
	Resources/config/form_types.xml
	Resources/doc/reference/form_types.rst
	Resources/views/Form/form_admin_fields.html.twig
	Tests/Datagrid/DatagridTest.php
	Tests/Form/DataTransformer/ModelToIdPropertyTransformerTest.php
	Tests/Form/Type/ModelAutocompleteTypeTest.php