Updated the marking of messages as new/read.

  We can now add a single flag to a message, which allows marking
 mail as new/read even if the mails aren't in new/ or cur/
  Added new stub class for file operations.

  This needs to be implemented, then used.

  This is part of issue #25.
  Updated to have stub-functionality.

  The code works, but needs to be rewritten.
  Use CFile::copy() + CFile::move().

  This makes things neater.