Github OAuth & Session Handling

[mririgoyen]

Proposed Changes

• Adds GitHub OAuth flow to the API.
• Adds Session handling endpoints to the API.
• Adds a placeholder Admin section into the client.
• Adds a temporary login page into the client.
• Adds an AuthProvider for handling sessions in the client.

Types of Changes

What types of changes does your code introduce?

• [ ] Documentation Update
• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• [x] I have read the Contributing doc.
• [x] Lint passes locally with my changes.
• [x] I have added necessary documentation (if appropriate).

Additional Information

The ability to login and logout are in the client now, but the links to do so from the UI are hidden because there really is nothing anyone can do when they are logged in at the moment. Therefore, I've hidden them to avoid confusion. Once we add some features that require logging in, we can enabled the header link.