Add error state to login and register forms

[daryllxd]

Hello, was just trying the repo out and when I forgot to start the API server, there was no clear error message. IMO app should show a message to if the users weren't able to log in or register, especially for newbies in React trying to figure a good app structure to base off of

• Add a simple error message for potential server errors for just the first two screens, login and register. (It could be more declarative, I just returned the actual error message for now).
• Needed to add className prop to Error to not make the error message too cramped.

Login	Register

Caveat

• Didn't add for the other forms yet and didn't add the tests yet

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