Add preliminary XMonad-support

Preliminary XMonad-support:
- re-linking of xmonad.hs-file
  NOTE: since we don't want to delete the compiled-files (in case
        there is a running XMonad-session), we just replace the
        configuration-file.

- new function 'relink_in_folder', to support the special linking

Refactoring:
- 'relink_to_home' -> 'relink_in_home' (and fix in description)