PicardTestCase: Reset config.setting in setUp

This helps finding tests that don't explicitly specify all settings they need.

test/picardtestcase.py

@@ -31,3 +31,4 @@ class FakeTagger(QtCore.QObject):
 class PicardTestCase(unittest.TestCase):
     def setUp(self):
         QtCore.QObject.tagger = FakeTagger()
+        config.setting = {}