Two factor authentication plugin using YubiKey

With this plugin you can use a YubiKey hardware token device (available from Yubico.com) for two-factor authentication in Joomla!. The OTP validation is performed against the YubiCloud servers.
SQL files for the YubiKey two factor auth plugin
Changed description of plg_twofactorauth_yubikey for greater clarity
Merge branch 'refs/heads/projects-master' into feature-twofactor-yubikey
Merge branch 'refs/heads/projects-master' into feature-twofactor-yubikey

Conflicts:
	administrator/components/com_admin/sql/updates/mysql/3.2.0.sql
	administrator/components/com_admin/sql/updates/postgresql/3.2.0.sql
Improved YubiKey handling

- Error message shown when you try to activate this feature but the OTP is invalid or doesn't validate against YubiCloud's servers
- Shuffle the list of YubiCloud servers, using a different, random one every time (helps spread out the load and improve the resilience of the implementation)
- Use a time based nonce instead of the form token to prevent YubiCloud responding with REPLAYED_OTP if the form token doesn't change between subsequent attempts
The YubiKey authentication would always return false
Merge branch 'refs/heads/cms-master' into feature-twofactor-yubikey

Conflicts:
	administrator/components/com_admin/sql/updates/mysql/3.2.0.sql
	administrator/components/com_admin/sql/updates/postgresql/3.2.0.sql
	administrator/components/com_admin/sql/updates/sqlazure/3.2.0.sql
	installation/sql/mysql/joomla.sql
	installation/sql/postgresql/joomla.sql
	installation/sql/sqlazure/joomla.sql
Merge pull request #1993 from joomla-projects/feature-twofactor-yubikey

Feature: Two Factor Authentication - YubiKey implementation