Merge changes from topics "async-challenge", "lss-sp"

* changes:
  Remove GenerateChallengeBlocking from FingerprintManager
  Change GenerateChallengeCallback from abstract class to interface
  3/n: Remove challenge from verifyCredential
  2/n: Remove unnecessary RequestThrottledException for verify paths
  1/n: Allow LockSettingsService to return Gatekeeper Password