further fixes of py3 issues

complaints by pylint are mainly related to
- remove object from base list in class definitions
- unnecessary else/elif after return/raise

Change-Id: I13d15449149cc8bba0562338d0c9c42e97163bdf
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21325
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/gui/nodectrl.py

@@ -25,6 +25,7 @@
 import json
 import pprint
 from time import sleep
+import mlzlog
 
 from secop.datatypes import EnumType, StringType
 from secop.errors import SECoPError
@@ -222,7 +223,6 @@ class ReadableWidget(QWidget):
         try:
             # if queried, we get the qualifiers as well, but don't want them
             # here
-            import mlzlog
             mlzlog.getLogger('cached values').warn(
                 'no cached value for %s:%s' % (self._module, pname))
             val = self._node.getParameter(self._module, pname)[0]