Merge branch 'thom/ispconfig3-5795-purge-apps-addons' into develop

install/lib/installer_base.lib.php

install/sql/incremental/upd_dev_collection.sql

install/sql/ispconfig3.sql

install/tpl/config.inc.php.master

install/tpl/security_settings.ini.master

interface/lib/config.inc.php

interface/web/admin/form/software_package.tform.php

interface/web/admin/form/software_repo.tform.php

interface/web/admin/lib/lang/ar_software_package.lng

interface/web/admin/lib/lang/ar_software_package_install.lng

interface/web/admin/lib/lang/ar_software_package_list.lng

interface/web/admin/lib/lang/ar_software_repo.lng

interface/web/admin/lib/lang/ar_software_repo_list.lng

interface/web/admin/lib/lang/ar_software_update_list.lng

interface/web/admin/lib/lang/bg_software_package.lng

interface/web/admin/lib/lang/bg_software_package_install.lng

interface/web/admin/lib/lang/bg_software_package_list.lng

interface/web/admin/lib/lang/bg_software_repo.lng

interface/web/admin/lib/lang/bg_software_repo_list.lng

interface/web/admin/lib/lang/bg_software_update_list.lng