make baseclient work without mlzlog

The used logger can now be configured from caller. This allows
for example to use NicosLogger when imported from NICOS.

+ fix a problem when connections was lost

Change-Id: I8496ba11ad467749493751b49c4e36dd739892ab
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21477
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/client/__init__.py

@@ -30,7 +30,10 @@ import threading
 from collections import deque
 from os import path
 
-import mlzlog
+try:
+    import mlzlog
+except ImportError:
+    pass # has to be fixed in case this file is used again
 
 from secop.protocol.interface import decode_msg, encode_msg_frame, get_msg
 from secop.protocol.messages import DESCRIPTIONREQUEST, EVENTREPLY