fixed bugs from syntax migration

- a new wrapper for a read function is not only to be created when
  the a new read method is in the class dict, but also when
  it is inherited, but not yet wrapped
- a handler must not be ignored, when a write method is inherited
- a proxy class must not call checkProperties

+ remove trailing spaces in tutorial_helevel.rst

Change-Id: I16024c14232ea200db91a1bc07ec23326219ab68
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/25093
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/proxy.py

@@ -122,6 +122,8 @@ class ProxyModule(HasIodev, Module):
                     self.announceUpdate(pname, None, readerror)
                 self.announceUpdate('status', newstatus)
 
+    def checkProperties(self):
+        pass # skip
 
 class ProxyReadable(ProxyModule, Readable):
     pass