ReadHandler and WriteHandler decorators

modules with a couple of parameters with similar read_* or
write_* methods may handle them by generic methods wrapped
with decorators ReadHandler / WriteHandler

The trinamic driver is included in this change for demonstrating
how it works.

In a further step, the special handling for the iohandler stuff can
be moved away from secop.server and secop.params, using this feature.

+ fix problem on startup of trinamic driver (needs MultiEvent.queue)
+ some other small fixes
+ apply recommended functools.wraps for wrapping

Change-Id: Ibfeff9209f53c47194628463466cee28366e17ac
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27460
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/persistent.py

@@ -103,6 +103,7 @@ class PersistentMixin(HasAccessibles):
                 try:
                     value = pobj.datatype.import_value(self.persistentData[pname])
                     pobj.value = value
+                    pobj.readerror = None
                     if not pobj.readonly:
                         writeDict[pname] = value
                 except Exception as e:
@@ -144,5 +145,6 @@ class PersistentMixin(HasAccessibles):
 
     @Command()
     def factory_reset(self):
+        """reset to values from config / default values"""
         self.writeDict.update(self.initData)
         self.writeInitParams()