[FEATURE] Add button to delete all mails and answers

[cweiske]

The "Mail list" page has a "cleanup" button that opens a small form
which allows one to delete all mails and answers on the current page.

Port of the old patch from 2018
#304

[hannesbochmann]

This would be a great feature. @cweiske The PR needs some refactoring to resolve the merge conflicts.

[hannesbochmann]

@cweiske I think those things need to be changed to make it work again:

• the translations are moved from the extension to the localization service of TYPO3. So the additions to de.locallang.xlf need to be added in another way. But I guess this is not that crucial.
• the ModuleController::deleteAllMailsBeAction() should return a ResponseInterface with "return new ForwardResponse('list');"
• in Resources/Private/Partials/Module/DeleteAllMails.html the form action should be "dispatch" and not "deleteAllMailsBe" and the form needs the element '<f:form.hidden name="forwardToAction" value="deleteAllMailsBe" id="forwardToAction" />'

[cweiske]

The original patch was 2018, the new one 2021. It's 6 years later now and I currently don't have a project that uses powermail. I won't update the patch in the forseeable future.