rework property handling

+ DataType validators are shifted to __call__
+ as_json is moved to export_datatape()
+ new HasProperties Base Mixin for Modules/DataTypes
+ accessibles can be accessed via iterator of a module
+ properties are properly 'derived' and checked, are set with .setPropertyValue

remember: parameters only have properties, so use getPropertyValue()

Change-Id: Iae0273f971aacb00fe6bf05e6a4d24a6d1be881a
Reviewed-on: https://forge.frm2.tum.de/review/20635
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/gui/modulectrl.py

@@ -131,8 +131,8 @@ class CommandButton(QPushButton):
         super(CommandButton, self).__init__(parent)
 
         self._cmdname = cmdname
-        self._argintype = cmdinfo['datatype'].argtype   # single datatype
-        self.resulttype = cmdinfo['datatype'].resulttype
+        self._argintype = cmdinfo['datatype'].argument   # single datatype
+        self.result = cmdinfo['datatype'].result
         self._cb = cb  # callback function for exection
 
         self.setText(cmdname)