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_demo/modules.py

@@ -155,11 +155,11 @@ class MagneticField(Drivable):
         if self._state == self._state.enum.idle:
             return (PERSIST, 'at field') if self.value else \
                    (self.Status.IDLE, 'zero field')
-        elif self._state == self._state.enum.switch_on:
+        if self._state == self._state.enum.switch_on:
             return (self.Status.PREPARE, self._state.name)
-        elif self._state == self._state.enum.switch_off:
+        if self._state == self._state.enum.switch_off:
             return (self.Status.FINISH, self._state.name)
-        elif self._state == self._state.enum.ramp:
+        if self._state == self._state.enum.ramp:
             return (self.Status.RAMPING, self._state.name)
         return (self.Status.ERROR, self._state.name)