Adds a plugin for managing a room's theme

I liked the plugin architecture of Lazy Susan and decided to start building out some additional functionality.  Here's my first little experiment, a plugin for managing the current theme (if any).

/theme => reply with the current theme (pm or spoken)
/themeset <blah> => set the theme and speak it to the room
/themeclear => remove the theme and announce it to the room

I'll hopefully have more as I get the hang of the internals of Lazy Susan and ttapi. :-)