Bridge custom emoji reactions as :custom:

Official web app doesn't support them yet either, this is probably
better than the raw UUID

libgm/gmproto/conversations.proto

@@ -55,11 +55,42 @@ enum EmojiType {
     CRYING_FACE = 10;
     POUTING_FACE = 11;
     RED_HEART = 12;
+    EMOTIFY = 13;
+}
+
+message CustomEmojiData {
+    message Inner {
+        optional string unknownString = 100;
+        message ImageData {
+            string mimeType = 1;
+            string uri = 2;
+            optional int32 unknownInt3 = 3;
+            optional string unknownString5 = 5;
+        }
+        message WrappedImageData {
+            message ImageData {
+                int32 unknownInt1 = 1;
+                string mimeType = 2;
+                string uri = 3;
+                int32 width = 5;
+                int32 height = 6;
+                optional int32 unknownInt7 = 7;
+            }
+            ImageData data = 1;
+        }
+        ImageData first = 101;
+        WrappedImageData second = 102;
+    }
+
+    string uuid = 1;
+    optional int32 unknownInt4 = 4;
+    Inner innerData = 100;
 }
 
 message ReactionData {
     string unicode = 1;
     EmojiType type = 2;
+    CustomEmojiData customEmoji = 101;
 }
 
 message EmojiMeta {

portal.go

@@ -798,8 +798,13 @@ func (portal *Portal) syncReactions(ctx context.Context, source *User, message *
 		remove[reaction.Sender] = reaction
 	}
 	for _, reaction := range reactions {
-		emoji := reaction.GetData().GetUnicode()
+		var emoji string
-		if emoji == "" {
+		switch reaction.GetData().GetType() {
+		case gmproto.EmojiType_EMOTIFY:
+			emoji = ":custom:"
+		case gmproto.EmojiType_CUSTOM:
+			emoji = reaction.GetData().GetUnicode()
+		default:
 			emoji = reaction.GetData().GetType().Unicode()
 			if emoji == "" {
 				continue