add get_server for admin/mod settings for modset help

cogs/utils/settings.py

@@ -49,6 +49,7 @@ class Settings:
 
     @prefixes.setter
     def prefixes(self,value):
+        assert isinstance(value,list)
         self.bot_settings["PREFIXES"] = value
         self.save_settings()
 
@@ -86,6 +87,10 @@ class Settings:
             ret.update({server:self.bot_settings[server]})
         return ret
 
+    def get_server(self,server):
+        assert isinstance(server,discord.Server)
+        return self.bot_settings.get(server.id,self.bot_settings["default"].copy())
+
     def get_server_admin(self,server):
         assert isinstance(server,discord.Server)
         if server is None: