Add better interface for getting and setting room tag account data.

Signed-off-by: Jason Volk <jason@zemos.net>

src/service/account_data/mod.rs

@@ -1,3 +1,5 @@
+mod room_tags;
+
 use std::sync::Arc;
 
 use futures::{Stream, StreamExt, TryFutureExt};