ext_localconf.php

<?php
if (!defined('TYPO3_MODE')) {
    die ('Access denied.');
}


call_user_func(
    function ($extKey) {

        \TYPO3\CMS\Extbase\Utility\ExtensionUtility::configurePlugin(
            'WapplerSystems.' . $extKey,
            'Pi1',
            array(
                'Flexslider' => 'list',
            ),
            // non-cacheable actions
            array()
        );

        \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPageTSConfig('<INCLUDE_TYPOSCRIPT: source="FILE:EXT:ws_flexslider/Configuration/TSconfig/ContentElementWizard.txt">');


        if (TYPO3_MODE === 'BE') {
            $icons = [
                'ext-wsflexslider-wizard-icon' => 'plugin_wizard.png',
                'ext-wsflexslider-image' => 'picture.png',
            ];
            $iconRegistry = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Core\Imaging\IconRegistry::class);
            foreach ($icons as $identifier => $path) {
                $iconRegistry->registerIcon(
                    $identifier,
                    \TYPO3\CMS\Core\Imaging\IconProvider\BitmapIconProvider::class,
                    ['source' => 'EXT:'.$extKey.'/Resources/Public/Icons/' . $path]
                );
            }
        }

    },
    'ws_flexslider'
);