FIXED MAGE-7242, FIXED MAGE-6336: Not display CAPTCHA if value zero ' Number of Unsuccess...

FIXED MAGE-7242: Not display CAPTCHA if value zero ' Number of Unsuccessful Attempts to Login ' in Backend
FIXED MAGE-6336: CAPTCHA is not shown at Login form

FIXES #62
FIXES #2

extended the _isShowAlways() method, to return true, either when the number of attempts is set to 0