PLT-2664 Split out push notifications from email notifications (#3049)

* Split out push and email notification logic, always send push notifications on mention

* Add user setting to control push notifications

* Minor changeto simplify code

webapp/i18n/en.json

@@ -1390,6 +1390,11 @@
   "user.settings.modal.notifications": "Notifications",
   "user.settings.modal.security": "Security",
   "user.settings.modal.title": "Account Settings",
+  "user.settings.push_notification.off": "Off",
+  "user.settings.push_notification.onlyMentions": "For mentions and direct messages",
+  "user.settings.push_notification.allActivity": "For all activity",
+  "user.settings.push_notification.info": "Notification alerts are pushed to your mobile device when there is activity in Mattermost.",
+  "user.settings.notification.push": "Mobile push notifications",
   "user.settings.notification.allActivity": "For all activity",
   "user.settings.notification.soundConfig": "Please configure notification sounds in your browser settings",
   "user.settings.notifications.channelWide": "Channel-wide mentions \"@channel\"",