add multiplexer/router

in case a remote is disconnected and can be reconnected quickly,
a seamless routing is possible. However, when after reconnection
the description has changed, the server is restarted.

+ more information in error messages from dispatcher

Change-Id: I0837e0254aee3d12a26481f6fd697081a53aabba
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/22506
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>

cfg/multiplexer.cfg

@@ -0,0 +1,7 @@
+[node router]
+type = router
+description = router node
+nodes = ['localhost:5000', 'localhost:10769']
+
+[interface tcp]
+bindto = 0.0.0.0:5001