Zend: Include Zend version 1.12.9

refs #7464
Zend: Remove require_once calls

refs #7464
Merge branch 'master' into feature/include-zend-7464
Zend: Reset require_once in Zend_Loader_Autoloader

refs #7464
Do not load Zend on the CLI and remove our library from the include path

Adding Icinga Web 2's library to the include is not necessary for getting the Zend_Plugin_Loader working.
Load Zend on Web and EmbeddedWeb

refs #7464
Merge branch 'feature/include-zend-7464'

resolves #7464