fix some remaining py3 incompatibilites

- None <= 0  is invalid in py3
- restrict BLOBType to bytes (may be changed after migration to py3)
- remove long
- use list(<dict>.items()) when dict is changed within loop
- allow initialization of properties in HasProperties without
  supercall to base class
- <dict>.values() can not be indexed
- adapted/removed various tests. additional tests might be added
  after definitive migration to py3

after this change, all the tests run with py3, also secop-server and
secop-gui were tested with an example, but other code might still contain
py3 incompatibilities

Change-Id: I881c6972aeabb8494a21a6cbc7ffeddfd4f5d4f8
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21306
Tested-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>
Reviewed-by: Bjoern Pedersen <bjoern.pedersen@frm2.tum.de>

secop/server.py

@@ -179,7 +179,7 @@ class Server(object):
             # following line is the reason for 'node' beeing the first entry in CFGSECTIONS
             if len(self.nodes) != 1:
                 raise ConfigError(u'cfgfile %r: needs exactly one node section!' % self._cfgfile)
-            self.dispatcher = self.nodes.values()[0]
+            self.dispatcher, = tuple(self.nodes.values())
 
         pollTable = dict()
         # all objs created, now start them up and interconnect