Add test for Zend_View_Helper_DateFormat

refs #6011
Move session tests to correct sub-folder

refs #6011
Add test for Icinga\Util\Translator

refs #6011
Add test for Icinga\Util\String

refs #6011
Move non-factory functions from DateTimeFactory to Icinga\Util\Format
Make DateTimeFactory expecting a string instead of a DateTimeZone
Add test for Icinga\Util\DateTimeFactory

refs #6011