Fix client-feature, no-model compiles

Some of the methods used in the client dispatch, namely `Channel::id`
and `Message::transform_content`, are not _required_ for functionality
by the dispatcher. Since these methods are `model` features, they can be
gated behind a `model` feature cfg.

src/client/dispatch.rs

@@ -112,7 +112,10 @@ fn dispatch_message(context: Context,
                     event_store: &Arc<RwLock<EventStore>>) {
     if let Some(handler) = handler!(on_message, event_store) {
         thread::spawn(move || {
-            message.transform_content();
+            #[cfg(feature="model")]
+            {
+                message.transform_content();
+            }
 
             (handler)(context, message);
         });
@@ -128,7 +131,15 @@ fn handle_event(event: Event,
         Event::ChannelCreate(event) => {
             if let Some(handler) = handler!(on_channel_create, event_store) {
                 update!(update_with_channel_create, event);
-                let context = context(Some(event.channel.id()), conn, data);
+
+                let mut channel_id = None;
+
+                #[cfg(feature="model")]
+                {
+                    channel_id = Some(event.channel.id());
+                }
+
+                let context = context(channel_id, conn, data);
 
                 thread::spawn(move || (handler)(context, event.channel));
             } else {
@@ -172,7 +183,14 @@ fn handle_event(event: Event,
         },
         Event::ChannelUpdate(event) => {
             if let Some(handler) = handler!(on_channel_update, event_store) {
-                let context = context(Some(event.channel.id()), conn, data);
+                let mut channel_id = None;
+
+                #[cfg(feature="model")]
+                {
+                    channel_id = Some(event.channel.id());
+                }
+
+                let context = context(channel_id, conn, data);
 
                 feature_cache! {{
                     let before = CACHE.read().unwrap().channel(event.channel.id());