Updated the icon in the toolbar

MainActivity.kt

override fun onResume() {
  super.onResume()
  
  // Determine the current auth state and place the right icon in the ImageView
  if (AWSProvider.identityManager.isUserSignedIn)
    mainToolbarLockIcon.setImageResource(R.drawable.ic_locked_24dp)
  else
    mainToolbarLockIcon.setImageResource(R.drawable.ic_unlocked_24dp)
  mainToolbarLockIcon.isClickable = true
  mainToolbarLockIcon.isFocusable = true
}