Remember device only called for verification

[keoghpe]

Hey, I noticed that users can't remember their device when they verify their installation, only when they perform a regular verification (remember_device is called from POST_verify_authy but not from POST_verify_authy_installation).

Is there a particular reason that it is this way? Would it be insecure adding it to POST_verify_authy_installation? If not, I can submit a PR adding this.