Support for Two Factor Authentication

[KeeperOfMaps]

Look at adding support for Two Factor Authentication via an app such as Google Authenticator.

https://medium.com/@richb_/easy-two-factor-authentication-2fa-with-google-authenticator-php-108388a1ea23

[KeeperOfMaps]

Hey @dpi209 , could you take a look at what I've done in 94-support-for-two-factor-authentication when you have a moment? Basically, I've put hooks in at various points to support actually adding the 2FA stuff in the next step. More support is needed to build the form for when 2FA is being set up (e.g., display the QR code, confirm it works, etc.).

If I've done it right, if/when this is merged, it won't break anything, but I'm don't want to create the pull request, just yet.

Many thanks in advance!