dired-do-delete: Allow to delete dirs recursively without prompts

dired-do-delete: Allow to delete dirs recursively without prompts

* lisp/dired.el (dired-delete-file): Accept 2 additional answers:
'all', to delete all directories recursively and no prompt anymore.
'quit', to cancel directory deletions (Bug#27940).
Show help message when user inputs 'help'.
(dired-do-flagged-delete): Bind locally dired-recursive-deletes
so that we can overwrite its global value.
Wrapp the loop within a catch '--delete-cancel to catch when
the user abort the directtry deletion.
* doc/emacs/dired.texi (Dired Deletion): Update manual.
* etc/NEWS (Changes in Specialized Modes and Packages in Emacs 26.1):
Announce this change.