Delete all or specific user data by command or during uninstallation

[porg]

Deleting user data shall be possible with either of these:

• command line argument like etesync-dav manage --deleteUserData [[email protected]]
  • empty argument or special keyword like all deletes all users
  • stating a specific user deletes only the specific one
• as part of the uninstall routine of an installer or package manager #57 the user is asked whether to also delete user data (in this case "all")