shared config (#67)

* Add shared_config to BotConfig

* Allow plugins to overwrite shared_config

disco/bot/bot.py

@@ -76,6 +76,7 @@ class BotConfig(Config):
     levels = {}
     plugins = []
     plugin_config = {}
+    shared_config = {}
 
     commands_enabled = True
     commands_require_mention = True
@@ -504,6 +505,9 @@ class Bot(LoggingClass):
             self.config.plugin_config_dir, name) + '.' + self.config.plugin_config_format
 
         data = {}
+        if self.config.shared_config:
+            data.update(self.config.shared)
+
         if name in self.config.plugin_config:
             data.update(self.config.plugin_config[name])