Feature: Secure file deletion about pgptool

[skarpushin]

@MaxMil69 no. Not yet.

UPDATE: I think we should add "Secure deletion" menu item which will actually explain that secure deletion issues and describe options:

1. Use RAM disk for temporarily decrypted files
2. In case of txt files -- use embedded editor which does not save files on disk and keep them in memory
3. Impl attempt to actually do this:
   3.1. Overwrite file with random bytes (to overcome compression), delete it and then create super large file that occupies the rest of the space -- that way remnant blocks will be finally overwritten
   3.2. Integrate with 3rd-party tool, i.e. on Windows -- SDelete tool

[skarpushin]

Secure deletion is not really easy and sometimes even possible. At least SSDs and NTFS will persist file modifications to other place so from application we cannot really securely delete file that easily. Overwriting file with random or zero bytes is not enough actually. See https://www.physicsforums.com/threads/is-secure-deletion-possible-in-java.818802/ for details.

"Overwriting files":

• https://stackoverflow.com/questions/858036/how-to-securely-delete-files-in-java
• http://www.java2s.com/example/java-utility-method/file-delete-nio/securedelete-file-file-e7878.html