Simplifies saving INI files. Icinga\File\Ini\IniWriter does already require an
instance of Icinga\Application\Config so it's obvious to give "Config" the
task to initialize the writer.. We do also have a central place to handle
creating missing ancestor directories now.
refs #8219
We do not want to override Zend_Form::setConfig() so this renaming is
required. set*Ini*Config() because ConfigForm::save() utilizes an ini-writer
to persist the configuration to disk.
refs #5525