Added notifications page and integrated with backend

[ctc-devops]

Authors:

What does this PR contain?

• on /notifications page, we added a table that lists out all the pending users with functionality to approve/decline
• in table header, there is the ability to approve all or decline all
• note: for some reason, when you sign up for an account, it takes you to the landing dashboard page. so you are able to access the /notification page. i think this is not right. however, when you log out and signin again, then you are prompted with "pending approval" and can't log in until you are approved. i don't think our code affect that (maybe it's a bug in auth redirect?). everything else works as normal (ex: if you decline all from the notification's page and you are signed in as the pending user, then you are kicked out to login page).

How did you test these changes?

pgadmin

Attach images (if applicable)

Closes #21

[ThatMegamind]

Looks good to us! (TLs + shadowees)