Add support for limited login

[greymag]

Starting v17.0.0 Facebook login will use Limited Login (blog post) if user didn't provide AdvertiserTracking permission, even if we call logIn() with tracking: .enabled in configuration.

See https://github.com/facebook/facebook-ios-sdk/issues/2375

TODO:

• [x] Support Limited Login
• [x] Support API calls (profile, picture, email) in Limited Login mode
• [x] Add description, warning and link to the documentation about this behavior. Server verification of token in Limited Login are also different.

Useful links:

• Advertiser Tracking Enabled

[greymag]

There are some support implementation issues that were essentially solved with a crutch.

See this comment and discussion.

[greymag]

Released in v2.0.0

[greymag]

Important note: I didn't implement full support for the Limited Login. Only a necessary support for SDK v17.0 automatic fall bask behaviour on iOS.