Add playlist, video and ad skeleton

backend/app/models/subjectTarget.model.js

@@ -0,0 +1,16 @@
+module.exports = mongoose => {
+  let schema = mongoose.Schema({
+      name: String,
+      keywords: []
+    },
+    { timestamps: true }
+  );
+
+  schema.method("toJSON", function() {
+    const { __v, _id, ...object } = this.toObject();
+    object.id = _id;
+    return object;
+  });
+
+  return mongoose.model("subjectTarget", schema);
+};