Provide contextual help on auth provider configuration
Summary:
Ref T1536.
- Move all the provider-specific help into contextual help in Auth.
- This provides help much more contextually, and we can just tell the user the right values to use to configure things.
- Rewrite account/registration help to reflect the newer state of the word.
- Also clean up a few other loose ends.
Test Plan: {F46937}
Reviewers: chad, btrahan
Reviewed By: chad
CC: aran
Maniphest Tasks: T1536
Differential Revision: https://secure.phabricator.com/D6247