[CHANGE] Enhance overall functionality and make usage of PEAR library optional

* Make PEAR usage (of Auth/Yubico.php) optional and provide native OTP
  verification by add class YubiKeyAuth for native OTP verification
* Update EM configuration options and provide new option to enable PEAR
  Is turned off by default to avoid PHP fatal errors
* Allow multiple YubiKeys for a single backend user
* Update source for TYPO3CMS CGL compliance