Removes need for app_id key

The config FILE can contain many SECTIONS. Each section is independent
and contains one client's details.

Possibly for detecting if the config was for an old API client or a new
User App, two keys were used for exactly the same thing the client_id
and secret passed to fog.

Being different they could be placed side by side in one config section
merging two clients with random behaviour.

This removes the "app" version of the keys which will break existing
configuration setup using a prerelease version of the CLI.
Renames username value from email

"email" is inaccurate since it can be a username like usr-12345 or an
email address. The OAuth option is again username.

This also slims down the 'options' passed to #fetch_refresh_tokens since
none are optional for it to work based on current implementation.
Sending blank values to fog will just trigger API errors.