Make PluginBase concrete

The abstract method really just wasn't working at all.  Since it doesn't
really hurt anything to be able to instantiate PluginBase, I just
forewent all the metaclass nonsense and made it a normal class.

kayleevc/plugins/pluginbase.py

 # Copyright 2015-2016 Clayton G. Hobbs
 # Portions Copyright 2013 Jezra
 
-from abc import ABCMeta, abstractmethod
-
 from gi.repository import GObject
-from gi.types import GObjectMeta
-
-
-class GObjectABCMeta(ABCMeta, GObjectMeta):
-    pass
 
 
-class PluginBase(GObject.Object, metaclass=GObjectABCMeta):
+class PluginBase(GObject.Object):
     """Base class for Kaylee plugins
 
     Each Kaylee plugin module must define a subclass of this class, named
         self.name = name
         self.corpus_strings = set()
 
-    @abstractmethod
     def recognizer_finished(self, recognizer, text):
         """Process a recognized voice command
 
         command will be handled, this method must emit a ``processed`` signal
         with ``text`` as its parameter.
         """
-        pass
+        return False