Fix EZP-20877: Improve unit test code coverage of eZ\Publish\Core\SignalSlot

Added the abstract class to test signal slot service
Fix EZP-20877:  Improve unit test code coverage of eZ\Publish\Core\SignalSlot

Added unit tests for the SignalSlot content service
Fix EZP-20877: Improve unit test code coverage of eZ\Publish\Core\SignalSlot

Added unit tests from SignalSlot content type service
Fixed CS issue
Fix EZP-20877: Improve unit test code coverage of eZ\Publish\Core\SignalSlot

Added unit test for SignalSlot section service
Fix EZP-20877: Improve unit test code coverage of eZ\Publish\Core\SignalSlot

Added unit tests for SignalSlot search service
 Fix EZP-20877: Improve unit test code coverage of eZ\Publish\Core\SignalSlot

Added unit test for SignalSlot language service
Fix EZP-20-877: Improve unit test code coverage of eZ\Publish\Core\SignalSlot

Added unit tests for SignalSlot field type service
Fix EZP-20877: Improve unit test code coverage of eZ\Publish\Core\SignalSlot

Added unit tests for SignalSlot location service
Fix EZP-20877:  Improve unit test code coverage of eZ\Publish\Core\SignalSlot

Added unit tests for the SignalSlot URL wildcard service