channel switcher for Lakeshore 370 with scanner

- add a general channel switcher module
- change ls370res code from IOHandler to rwhandlers
+ fix an issue with the poller when io module is placed below
  using modules in cfg file

after this, IOHandler stuff may be removed from Frappy

Change-Id: I787101fc1e365ae3e0453bfe59291e2011a1fe53
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/28512
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>

Makefile

@@ -38,7 +38,7 @@ doc:
 	$(MAKE) -C doc html
 
 lint:
-	pylint -j 0 -f colorized -r n --rcfile=.pylintrc secop secop_* test
+	pylint -f colorized -r n --rcfile=.pylintrc secop secop_* test
 
 isort:
 	@find test -name '*.py' -print0 | xargs -0 isort -e -m 2 -w 80 -ns __init__.py