Added email sign in option

[kjasani111]

Summary
This pull request supports email sign in through Firebase UI. It also removes Google sign-in. This will hopefully fix the issue with Apple where we were required to add Apple sign-in if we had Google sign-in in order to push to the app store.

How it works now

• When the user presses 'get started,' a getStarted method is triggered that presents a Firebase UI window where the user can sign in with their email address.
• The Firebase UI comes with an authentication extension that was added to the LogIn view controller that automatically checks whether the user had an account previously or not, and automatically creates an account with the user's email, or logs the user in to their existing account.
• The uid of the logged in user is passed into the get server auth token, which validates the token and returns another token generated by Django. If this token is valid, then the user is successfully logged in.
• In order to implement these changes, I had to update the API key (the other one was expired).

Test Plan
-The test plan is to run the new sign in with the backend server and see if a servertoken is appropriately generated.

Breaking Changes
-Users will not be using google sign in

[dti-github-bot]

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