Rename actor.py to backend.py to be more in line with other plugins

mopidy_gmusic/__init__.py

@@ -42,7 +42,7 @@ def get_config_schema(self):
         return schema
 
     def setup(self, registry):
-        from .actor import GMusicBackend
+        from .backend import GMusicBackend
         from .scrobbler_frontend import GMusicScrobblerFrontend
         registry.add('backend', GMusicBackend)
         registry.add('frontend', GMusicScrobblerFrontend)

tests/test_extension.py

@@ -3,7 +3,7 @@
 import mock
 
 from mopidy_gmusic import (
-    GMusicExtension, actor as backend_lib, scrobbler_frontend)
+    GMusicExtension, backend as backend_lib, scrobbler_frontend)
 
 
 class ExtensionTest(unittest.TestCase):

tests/test_library.py

@@ -1,6 +1,6 @@
 import unittest
 
-from mopidy_gmusic import actor as backend_lib
+from mopidy_gmusic import backend as backend_lib
 
 from tests.test_extension import ExtensionTest