Use jdenticon for default avatars (#416)

package.json

@@ -23,6 +23,7 @@
     "cssnano": "^5.1.15",
     "dayjs": "^1.11.9",
     "github-markdown-css": "^5.5.0",
+    "jdenticon": "^3.3.0",
     "nodemon": "^2.0.22",
     "postcss": "^8.4.32",
     "postcss-cli": "^11.0.0",