extract method to prepare for transforming singular files in arrays
made the directories protected
the email is persisted
the installer pushes its IO exception to the caller
The whole thing is not testable, therefore these prints help with manual testing :)
Fixed weird behaviour (under linux?)

Files.write(... StandardOpenOption.CREATE) behaved strangely under linux (it left parts of the old file contents instead of a clean rewrite).

To make sure this odd thing does not happen, the old files now get deleted first.

Java's believe it or not ..