Made PhysicalFilesystemAccessObjectTest extend from LunrBaseTest instead of PHPUnit framework directly.
The following files are related to the above and therefore their methods have been updated, where useful.
PhysicalFilesystemAccessObjectBaseTest
PhysicalFilesystemAccessObjectDirectoryTest
PhysicalFilesystemAccessObjectFindTest
PhysicalFilesystemAccessObjectListDirectoriesTest
PhysicalFilesystemAccessObjectListFilesTest
PhysicalFilesystemAccessObjectTest
On the other hand, PhysicalFilesystemAccessObjectFileTest was relevant but didn't need change.
