Notification - Update the Notification page in the MEFE

[franck-boullier]

This is the 'simplest' notification mechanism (See issue #185 for more details about notification about cases)

We need to implement the design described here:
https://projects.invisionapp.com/d/main#/console/12250377/262088035/preview

@kiatlim we might need to revisit that to:

• Add the possibility to delete/hide the notifications which have already been seen by a user (how can we do that?)
• Clarify that when a user clicks/taps on a notification then he/she is sent to the case that is relevant to this notification.

@nbiton I am tentatively putting this in the June 10th Milestone until further notice...