Add unit test for /account/2fa BadTokenException handling
Add unit test for /account/2fa BadTokenException handling

And some improvements from code review

micahflee/securedrop,micahflee/securedrop,ageis/securedrop,ageis/securedrop,micahflee/securedrop,ageis/securedrop,ehartsuyker/securedrop,garrettr/securedrop,ageis/securedrop,conorsch/securedrop,conorsch/securedrop,heartsucker/securedrop,conorsch/securedrop,garrettr/securedrop,heartsucker/securedrop,heartsucker/securedrop,conorsch/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,garrettr/securedrop,micahflee/securedrop,heartsucker/securedrop,garrettr/securedrop,conorsch/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop