fix debian files

to work again (hopefully).

Also:
 - few minor tweaks for py3
 - added psi facility
 - split secop-gui into separate package, so secop-core doesn't need QT

Change-Id: I457d3c9c60c78feb40e15c2fb153ce0d3491d1e8
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21327
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Tested-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>

etc/secop-generator

@@ -1,5 +1,4 @@
-
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #  -*- coding: utf-8 -*-
 # *****************************************************************************
 # Copyright (c) 2015-2019 by the authors, see LICENSE

etc/secop-server

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #  -*- coding: utf-8 -*-
 ### BEGIN INIT INFO
 # Provides: secop-server