URN for image info (#78)

* Allow music service to return a URN identifying cover art for an entity

* Fix bug with playlist cover art rending same album multiple times

package.json

@@ -13,6 +13,7 @@
     "@types/jws": "^3.2.4",
     "@types/morgan": "^1.9.3",
     "@types/node": "^16.7.13",
+    "@types/randomstring": "^1.1.8",
     "@types/sharp": "^0.28.6",
     "@types/underscore": "^1.11.3",
     "@types/uuid": "^8.3.1",
@@ -27,11 +28,13 @@
     "libxmljs2": "^0.28.0",
     "morgan": "^1.10.0",
     "node-html-parser": "^4.1.4",
+    "randomstring": "^1.2.1",
     "sharp": "^0.29.1",
     "soap": "^0.42.0",
     "ts-md5": "^1.2.9",
     "typescript": "^4.4.2",
     "underscore": "^1.13.1",
+    "urn-lib": "^2.0.0",
     "uuid": "^8.3.2",
     "winston": "^3.3.3"
   },