Moved middleware/ & schemas/ into api/.

api/schemas/Subscription.js

@@ -0,0 +1,13 @@
+const mongoose = require("mongoose");
+const Schema = mongoose.Schema;
+
+const Subscription = new Schema({
+  endpoint: String,
+  expirationTime: Number,
+  keys: {
+    p256dh: String,
+    auth: String
+  }
+});
+
+module.exports = mongoose.model("Subscription", Subscription);