Get plugin options in PluginBase

To reduce the boilerplate code needed for each plugin, the PluginBase
class now pulls out the plugin's options from the configuration object.
They get stored under the reasonably obvious name of ``options``.

kayleevc/plugins/pluginbase.py

         super().__init__()
         self.config = config
         self.name = name
+        self.options = config.options.plugins[name]
         self.corpus_strings = set()
 
     def recognizer_finished(self, recognizer, text):

kayleevc/plugins/shell.py

 
     def __init__(self, config, name):
         super().__init__(config, name)
-        self.options = vars(self.config.options)
         self.number_parser = NumberParser()
-        self.commands = self.options['plugins'][name]
+        self.commands = self.options
 
         for voice_cmd in self.commands.keys():
             self.corpus_strings.add(voice_cmd.strip().replace('%d', ''))