Improvement: Custom Notifications

[adnan-sami-raiyan]

Enable the organiser to create custom notifications, while still having the ability to send a pre-built notification.

Potential implementation:

• have the pre-built notification a pre-existing text that pops up when the "Notify" button is clicked
• allow the organiser to edit that pre-existing text, or simply send it as it is.

NB: There needs to be "Notify" button in 2 screens based on organiser user stories:

• Manage Waitlist
• Result List