new poll mechanism

- remove secop.poller and basic poller
- regular polls for 'important' parameters done by method doPoll
- all other parameters are polled slower (slowInterval) and
  with lower priority (only one at a time when main poll is due)
- nopoll decorator for read_* to disable poll
- enablePoll attribute (default True) for disabling polling a module
- fast polls may be implemented by means of a statemachine
- configurable slow poll interval
+ allow a Parameter to override a Property (parameter
  Readable.pollinterval overrides Module.pollinterval)

Change-Id: Ib1b3453041a233678b7c4b4add22ac399670e447
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27832
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>

secop/lib/sequence.py

@@ -153,7 +153,7 @@ class SequencerMixin:
             self._seq_error = str(e)
         finally:
             self._seq_thread = None
-            self.pollParams(0)
+            self.doPoll()
 
     def _seq_thread_inner(self, seq, store_init):
         store = Namespace()