Add nice looking toasts instead of using alerts

[tko22]

There a couple libraries for react toasts to choose from:

• https://github.com/fkhadra/react-toastify
• https://tomchentw.github.io/react-toastr/
• https://www.npmjs.com/package/react-toasts

First, replace many of the alerts with toasts and find different places where adding a toast notification would be nice. A couple places on top of my head...

• Logging in/out
• Wrong credentials
• Successfully/Failing adding an interview