Add qr and inapp namespaces for app verification

[chrisfisher]

Breaking Changes

• 2.0.0-alpha1 release
• Remove generic device namespace for all app verification flows. Introduce qr and inapp alongside push to use instead.
• The push.getCredential method nows returns AuthsignalResponse<AppCredential> instead of AuthsignalResponse<PushCredential>.
• The push.addCredential method now returns AuthsignalResponse<AppCredential> instead of AuthsignalResponse<Bool>.

New Features

• Introduce qr and inapp namespaces with methods for QR code and in-app verification flows.

Checklist

• Version bumped
• Documentation updated