Implement 2 factor authentication

[crossan007]

trafficstars

http://blog.meldium.com/home/2013/8/23/screw-up-two-factor-authentication

[BethaniaLC]

While we have very robust passwords for the CRM it would be safer if a free 2FA could be included as standard after all it is a lot of sensitive data.

[crossan007]

see #4656

[respencer]

Dead link, here's the archived copy:

https://web.archive.org/web/20180507113115/http://blog.meldium.com:80/home/2013/8/23/screw-up-two-factor-authentication

[respencer]

While we have very robust passwords for the CRM it would be safer if a free 2FA could be included as standard after all it is a lot of sensitive data.

Unfortunately we don't have robust passwords. We need this, and the password hash issue (#3042) needs to be addressed.

[respencer]

Implemented in: f0be3fd