Spring fullstack Addressbook with Oauth

[richiethom]

In this PR I have created an Oauth version of the Spring Fullstack Addressbook, set up to work with Google. I haven't tried other Oauth providers such as MS. It isn't perfect but it works.

I have based myself a lot on the guidance you gave in this issue, and have tried to formalise things a bit in their own sample.

Main changes:

• removed passwords from the code and database where possible
• Frontend
  • removed all the signup code, we now just redirect to the
  • added a proxy entry for the backend to let the call to the backend for oauth go through
• Backend
  • Added depedencies to Spring's Oauth
  • Changed the build script to allow passing the secrets through
  • Changed the Security class to use Oauth

Please let me know what you think. I have added a few comments to explain what has happened.