Removes Support for sg_seo < 5.0

[FEATURE] Allow more than one company assignment, Fix broken mail sending of unsolicited applications

[FEATURE] Add link to allow external job application URLs, some cleanup, TCA restructured a little bit

https://trello.com/c/3ocgBvPZ/3021-websitebase-alle-erweiterungen-pr%C3%BCfen-und-anpassen-des-tca-f%C3%BCr-syslanguageuid-und-auto-code-format-der-ide-in-den-tca-dateien

[TASK] Remove exclude for l10n_parent field, because it causes bugs with translations in limited be-accounts