Make notifications cancellable

This commit makes certain notifications cancellable. This enables notifications to be sent conditionally based on the user's choice.

app/Traits/Cancellable.php

@@ -0,0 +1,49 @@
+<?php
+
+
+namespace App\Traits;
+
+
+use App\Facades\Options;
+
+trait Cancellable
+{
+
+    public function chooseChannelsViaOptions()
+    {
+        $channels = [];
+
+        if (Options::getOption('enable_slack_notifications') == 1)
+        {
+            array_push($channels, 'slack');
+        }
+        elseif(Options::getOption('enable_email_notifications') == 1)
+        {
+            array_push($channels, 'email');
+        }
+
+        return $channels;
+    }
+
+    public function channels()
+    {
+        return ['mail'];
+    }
+
+    public function via($notifiable)
+    {
+        if ($this->optOut($notifiable))
+        {
+            return [];
+        }
+
+        return $this->channels();
+    }
+
+
+    public function optOut($notifiable)
+    {
+        return false;
+    }
+
+}