Refactored ThingManager to support "virtual" channels.

At the moment the ThingManager can only delegate to the thing handler if the channel exists at a thing, which is determined by getChannels(). However there might use cases where a binding wants to support a "virtual" channel. The ItemChannelLink mechanism allows to bind such virtual channels. With this PR the ThingManager delegates each command and update to the ThingHandler, regardless if the Thing defines an according channel or not. 

Moreover the logging is optimized with this PR.

Signed-off-by: Dennis Nobel <d.nobel@external.telekom.de>