Channels: Include last message id on text channels.

API: Return members when fetching messages.
Misc: Remove defunct DISABLE_REGISTRATION variable.

src/routes/servers/channel_create.rs

@@ -60,6 +60,7 @@ pub async fn req(user: User, target: Ref, info: Json<Data>) -> Result<JsonValue>
         name: info.name,
         description: info.description,
         icon: None,
+        last_message: None
     };
 
     channel.clone().publish().await?;