Update messages

Come to think of it, "topic" is a better description (in English, at least) for the concept than "discussion" is, as discussion implies a free-flowing conversation.

You may want to check out comments in translation_context (Ctrl+F for "//") that highlight a number of strings that have now been removed. However, it is up to you whether to deprecate them or not as some (like spectatorRoom) may prove useful in the future.

I know this is not the best way to leave a message to you about this, but meh, I'm pretty confident you'll read it anyway :)