Allow plugin registration using a decorator as well.

For example:

    @plugin_pool.register_plugin
    class DecoratorTestPlugin(CMSPluginBase): ...

Author: qris

cms/plugin_pool.py

@@ -106,6 +106,8 @@ def register_plugin(self, plugin):
             except RegistrationError:
                 pass
 
+        return plugin
+
     def unregister_plugin(self, plugin):
         """
         Unregisters the given plugin(s).

cms/tests/plugins.py

@@ -1092,6 +1092,13 @@ def test_plugin_translatable_content_getter_setter(self):
         # double check through the getter
         self.assertEqual({'body': "It works!"}, plugin.get_translatable_content())
 
+    def test_plugin_pool_register_returns_plugin_class(self):
+        @plugin_pool.register_plugin
+        class DecoratorTestPlugin(CMSPluginBase):
+            render_plugin = False
+            name = "Test Plugin"
+        self.assertIsNotNone(DecoratorTestPlugin)
+
 
 class FileSystemPluginTests(PluginsTestBaseCase):
     def setUp(self):