Improve 2FA

[mennodekker]

Followup for #237

• [x] Allow to disable or reset 2 factor for a user by the admin
• [ ] Only allow to enable when a correct code was entered first
• [ ] Add a link to appstores for easier installation: https://play.google.com/store/apps/details?id=com.google.android.apps.authenticator2 https://itunes.apple.com/app/google-authenticator/id388497605?mt=8
• [ ] Add a help page that explains how this works to the user
• [ ] Add installation guidance in the wiki
• [x] Stop using the charts.google api, maybe use https://github.com/endroid/qr-code

[mennodekker]

@mddejong @jvangestel I opened this ticket for improvements in a future version of 2FA, feel free to add

[mennodekker]

https://realhosting.nl/helpdesk/controle-paneel-beveiligen-met-google-authenticator-2fa/ has some inspiration for improvement: When setting up 2fa ask for the password again, so an unlocked computer does not allow strangers to lock you out

[mennodekker]

https://play.google.com/intl/en_us/badges/ https://linkmaker.itunes.apple.com/nl-nl/details/388497605?country=nl&mediaType=ios_apps&term=google+authenticator&type=ipadsoftware

[mennodekker]