Show auth error

[chidimo]

What does this PR do?

Improve user experience

Description of Task to be completed?

• Display API call errors to user during sign in, sign up, and profile edit
• Display loading circle during API call.

How should this be manually tested?

Frontend test

1. Clone the repo
2. Open /UI/authentication.html in a browser
3. Click the sign in or sign up tab.
4. Enter the required credentials. You should see a loading circle while the API call is being made, and a visible display of any error encountered..

Any background context you want to provide?

Nil

What are the relevant pivotal tracker stories?

166397037

Screenshots (if appropriate)

Nil

Questions:

Nil