Pass at media server implementation

Still need to figure out client-server for this but it seems reasonable
right now. Need to figure out if everything should be boxed slices or
Vecs as well

src/client.rs

@@ -225,6 +225,9 @@ pub enum ClientMessage {
         #[serde(with = "serde_bytes")]
         bytes: Vec<u8>
     },
+    MediaFetch {
+        id: Uuid,
+    },
     // Join and subscribe
     RoomJoin {
         room_id: RoomId,
@@ -344,7 +347,9 @@ pub enum ServerMessage {
     // Returned on fetch or naturally from subscribe
     // This should be 
     Messages(Vec<TaggedMessage>),
-    MediaUploaded(Uuid),
+    MediaId(Uuid),
+    #[serde(with = "serde_bytes")]
+    Media(Box<[u8]>),
     Error(ServerError),
     // Returned on read
     State(StatePath,StateValue),