Added room topics and autodeclare

New commands /roomtopic and /autodeclare, based on an idea expressed in the PiratePad. Roomtopic is like roomdesc but instead of being called with ! by a voiced user or above, roomtopics are automatically shown to users when they join the room, like how the modchat level is displayed. The command "/autodeclare on" is used to turn on this feature, while "/autodeclare off" simply turns it off. Roomowners set the topic with the command "/roomtopic"; it allows images and clickable links if you use tags that are used with "/declare".