Make OAuth client authorizations a Settings panel

Summary: This modernizes and simplifies OAuth client authorizations a bit, moving them to a settings panel similar to the "Sessions" panel.

Test Plan:

• Viewed authorizations.
• Revoked an authorization.
• Created a test authorization.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8561