Removed debug logging.
These lines used for debug were committed by mistake in commit 3c32ac04f2ceb0068ce5d38f918079fa11965bca.
Allowed for asynchronous message for linknx.
linknx.sendMessage had always been synchronous before today. This was
anticipated to be an issue with <execute> request, as executeAction
would always have waited for action's completion before returning. In
most cases, client would certainly not care about the status
(success/failed) of its action as pyknx/linknx interactions are
naturally asynchronous. For that, executeAction does now use an
asynchronous version of sendMessage that uses a thread to perform the
request. In that version, there is no way for the client to get linknx's
answer. A callback may be added in the future to enhance that.