#166815539 fix bug user read unread notification

[Inclet]

What does this PR do?

This PR retrieve notification of a user and sort them by unread ones.

Description of Task to be completed?

• Included an attribute of sorting notifications as an instance method of notification model.

How should this be manually tested?

• Clone this repo https://github.com/andela/strikers-ah-backend.git
• Open a folder where you cloned this repo and open Terminal/cmd there.
• Checkout to develop branch by typing git checkout develop in your opened terminal.
• Type npm install to install all dependencies needed for this app.
• Type npm start to start the server.
• To see all notification you can access localhost:5000/api/profiles/notifications route through postman.

Any background context you want to provide?

• Use postman chrome extension to access app routes.

What are the relevant pivotal tracker stories?

#166815539

Screenshots (if appropriate)

[mwibutsa]

Fix the Travis issues and let us know