Upgrade devise, devise-two-factor, and attr_encrypted

Devise (3.5.4 => 4.1.1) Changelog: https://github.com/plataformatec/devise/blob/master/CHANGELOG.md

devise-two-factor (2.0.1 => 3.0.0) Changelog: https://github.com/tinfoil/devise-two-factor/blob/master/CHANGELOG.md

attr_encrypted (1.3.4 => 3.0.1) Changelog: https://github.com/attr-encrypted/attr_encrypted/blob/master/CHANGELOG.md

Devise 4 includes support for Rails 5, working towards #14286 (moved). devise-async doesn't support Devise 4.0 and in 4.1 the bug that was blocking using Devise's built-in ActiveJob integration was fixed. So devise-async is removed. devise-two-factor 3.0.0 is required for Devise 4 support.

attr_encrypted and encryptor are optional but recommended upgrades for devise-two-factor 3.0.0. The mode and algorithm will need to be changed in order to update to attr_encrypted 4.x in the future.

cc: @rspeicher