merge 'parameters' and 'commands' to 'accessibles'

- for now, the definition also accepts the old syntax
  (to be changed later)
- Commands have datatype CommandType
- do not need keyword for the decription parameter of Override
- issue a Warning when a Parameter is overwritten without Overrride
  (this should be turned into an error message)
-

Change-Id: Ib2c0f520abb5b4d7e6aed4d77a0d2b8bc470a85a
Reviewed-on: https://forge.frm2.tum.de/review/18251
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/gui/modulectrl.py

@@ -127,8 +127,8 @@ class CommandButton(QPushButton):
         super(CommandButton, self).__init__(parent)
 
         self._cmdname = cmdname
-        self._argintypes = cmdinfo['arguments']   # list of datatypes
-        self.resulttype = cmdinfo['resulttype']
+        self._argintypes = cmdinfo['datatype'].argtypes   # list of datatypes
+        self.resulttype = cmdinfo['datatype'].resulttype
         self._cb = cb  # callback function for exection
 
         self.setText(cmdname)