Add logging

[Chimstaz]

Add logging over MQTT on specified channel. It will be good if there will be option to specify level of logging. One proposition is to add in root of configuration packet key "type". If value of type is "Hardware" then do dispatching as it is now. If value of type is "Logging" then add key "Level" with values from set {DEBUG, ERROR, INFO}.

According to #3 prints should utilize new logging mechanic.

[maxiwoj]

I think it would be great, to have both logging through Serial port (Log level can be set as constant in the code) and logging through mqtt broker for runtime error alerts and remote debugging - this should be possible to set remotely

[Chimstaz]

Both logging strategy should be included. Maybe Debug level should include option to disable via define in compilation time? It will save some time on release version of application. As stated in #13 only option to publish at the moment is QoS 0. It will be nice, if log message include ID of message to not get lost while debugging when some messages will be dropped.