Convert usermods from header to library

usermods/pixels_dice_tray/library.json

@@ -0,0 +1,9 @@
+{
+  "name:": "pixels_dice_tray",
+  "build": {
+    "srcDir": ".",
+    "includeDir": "../../wled00",
+    "libLDFMode": "chain+",
+    "libArchive": false
+  }
+}

usermods/pixels_dice_tray/pixels_dice_tray.cpp

@@ -533,3 +533,7 @@ class PixelsDiceTrayUsermod : public Usermod {
   // extended. Your usermod will remain compatible as it does not need to
   // implement all methods from the Usermod base class!
 };
+
+
+static PixelsDiceTrayUsermod pixels_dice_tray;
+REGISTER_USERMOD(pixels_dice_tray);