hplip: stop installing corrupted tools

None of the installed tools like hp-align or hp-toolbox could
work, because they tried to import wrapped Python scripts (i.e.
shell code) as Python modules. Fix this by:

- Substituting `dbus` for the defective `pythonDBus`.

- No longer blindly wrapping all python files, but replacing
  the original symlinks in $out/bin with wrapper scripts.
  These wrappers then `exec` the unmodified Python scripts in
  $out/share/hplip directly, instead of the .<name>-wrapped
  copy that wrapPythonProgramsIn creates. The latter are simply
  removed.

Sure, it's a bit ugly. It's also 2015 and I couldn't use my
printer :-/