use Properties from secop.properties for datatypes

this change is triggered by the fact, that assigining a unit
in the config file did no longer work.

this change has several implications:
1) secop.properties must not import secop.datatypes:
   - as ValueType can not be imported, the default behaviour with
     'mandatory' and 'default' arguments was slightly changed
   - instead of checking for DataType when exporting, a try/except
     was used
2) the datatype of datatype properties is sometimes not yet defined.
   a stub is used in this cases instead, which is later replaced by
   the proper datatype. The number of stubs may be reduced, but this
   should be done in a later change, as the diff will be much less
   readable.
3) in config files, datatype properties can be changed like parameter
   properties. HasProperties.setProperties/checkProperties/getProperties
   are overridden for this.

the config editor seems still to work, an issue (probably py3) had
to be fixed there

Change-Id: I1efddf51f2c760510e913dbcaa099e8a89c9cab5
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21399
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/protocol/interface/tcp.py

@@ -200,11 +200,12 @@ class TCPServer(HasProperties, socketserver.ThreadingTCPServer):
     # XXX: create configurables from Metaclass!
     configurables = properties
 
-    def __init__(self, name, logger, options, srv):
+    def __init__(self, name, logger, options, srv): # pylint: disable=super-init-not-called
         self.dispatcher = srv.dispatcher
         self.name = name
         self.log = logger
-        HasProperties.__init__(self, supercall_init=False)
+        # do not call HasProperties.__init__, as this will supercall ThreadingTCPServer
+        self.initProperties()
         bindto = options.pop('bindto', 'localhost')
         bindport = int(options.pop('bindport', DEF_PORT))
         detailed_errors = options.pop('detailed_errors', False)