Notifications: Upcoming events

[swathi-ssunder]

• [x] Notification framework to send push notifications to the devices
• [x] Get a Notification with welcome message upon entering Mensa
• [x] Get a Notification with exit message upon leaving Mensa
• [x] Get notification immediately when an Event or Menu is added
• [ ] Mark an event that you are interested
• [x] Get a reminder on the day of event (or a day before)

[swathi-ssunder]

Framework for Notifications implemented - refer 5d41a467117588d1481503e84a9d696da2daca2b

[swathi-ssunder]

Notifications on entry & exit to the Mensa, Notification about today's event - refer https://github.com/swathi-ssunder/diy-net/pull/42

[swathi-ssunder]

Mark an event that you are interested - Refer #48