Merge branch 'feature_sg_mail' into 'master'

Classes/Command/SendMailCommandController.php

Classes/Controller/MailController.php

Classes/Domain/Model/Mail.php

Classes/Domain/Repository/AbstractRepository.php

Classes/Domain/Repository/MailRepository.php

Classes/Service/MailTemplateService.php

Classes/ViewHelpers/AbstractViewHelper.php

Classes/ViewHelpers/Be/Menus/ActionMenuItemViewHelper.php

.../ViewHelpers/Be/Menus/ActionMenuOptionGroupViewHelper.php

Classes/ViewHelpers/ExtendedIfViewHelper.php

Classes/ViewHelpers/InlineLanguageLabelsViewHelper.php

Configuration/TCA/tx_sgmail_domain_model_mail.php

Configuration/TypoScript/constants.ts

Configuration/TypoScript/setup.ts

Resources/Private/Language/de.locallang.xlf

Resources/Private/Language/de.locallang_db.xlf

Resources/Private/Language/locallang.xlf

Resources/Private/Language/locallang_db.xlf

Resources/Private/Layouts/Default.html

Resources/Private/Templates/Index.html