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>

cfg/ls370sim.cfg

@@ -5,19 +5,24 @@ description = Lsc Simulation at PSI
 [INTERFACE]
 uri = tcp://5000
 
-[res]
-class = secop_psi.ls370res.ResChannel
-channel = 3
-description = resistivity
-main = lsmain
-io = lscom
-
-[lsmain]
-class = secop_psi.ls370res.Main
-description = main control of Lsc controller
-io = lscom
-
 [lscom]
 class = secop_psi.ls370sim.Ls370Sim
 description = simulated serial communicator to a LS 370
 visibility = 3
+
+[sw]
+class = secop_psi.ls370res.Switcher
+description = channel switcher for Lsc controller
+io = lscom
+
+[a]
+class = secop_psi.ls370res.ResChannel
+channel = 1
+description = resistivity
+switcher = sw
+
+[b]
+class = secop_psi.ls370res.ResChannel
+channel = 3
+description = resistivity
+switcher = sw