Extracted user form tabs to a shared template to avoid duplication. Some legacy leftover code removed from act_edit_security.php.
Added UI method selection. Form splitted into smaller templates for easier maintenance.
Moved disabling functionality to 'none' tab and removed disable button from GA.
adminModule now can store and retrieve all three options of authentication (none, GA, YubiKey).
Added new security functionality and templates to home section (user preference panel).
Moved template strings to gettext calls. Added some extra information to YubiKey form.
Added Yubico.php 3rd party library. Added API configuration to config template. Added yubikey code check to login flow.
Added an extra control on user's preferences to prevent Yubikey auth being activated if system's yubico API is not configured.
Added 2Step auth column to administrator's user list view.
Added API key check to user's preference pane. Could not avoid code duplication a per current architecture =/
Added YubiKey-user pairing to user's preferences.
Merge pull request #1 from txau/yubikey

Yubikey
Added a hint to the wrong code feedback message in Google Auth configuration screen to check time correction for codes in app settings since this is the common cause for GA not working
Solved a bug in Google Authenticator setup, field name for code was conflicting with YubiKey's. Moved TSV method feedback message above the tabs.
Merge pull request #2 from txau/yubikey

GA fix merge