Fixes: Collection creation notification email

Added: Unsubscribe option to notification email footers
Added: Two new notification types (emails not written yet)
Fixed: Validation added to notification setting events

server/models/NotificationSetting.js

@@ -1,4 +1,5 @@
 // @flow
+import crypto from 'crypto';
 import { DataTypes, sequelize } from '../sequelize';
 
 const NotificationSetting = sequelize.define(
@@ -11,14 +12,42 @@ const NotificationSetting = sequelize.define(
     },
     event: {
       type: DataTypes.STRING,
+      validate: {
+        isIn: [
+          [
+            'documents.publish',
+            'documents.update',
+            'collections.create',
+            'emails.onboarding',
+            'emails.features',
+          ],
+        ],
+      },
     },
   },
   {
     timestamps: true,
     updatedAt: false,
+    getterMethods: {
+      unsubscribeUrl: function() {
+        const token = NotificationSetting.getUnsubscribeToken(this.userId);
+        return `${process.env.URL}/api/notificationSettings.unsubscribe?token=${
+          token
+        }&id=${this.id}`;
+      },
+      unsubscribeToken: function() {
+        return NotificationSetting.getUnsubscribeToken(this.userId);
+      },
+    },
   }
 );
 
+NotificationSetting.getUnsubscribeToken = userId => {
+  const hash = crypto.createHash('sha256');
+  hash.update(`${userId}-${process.env.SECRET_KEY}`);
+  return hash.digest('hex');
+};
+
 NotificationSetting.associate = models => {
   NotificationSetting.belongsTo(models.User, {
     as: 'user',