Fix a bug with concurrent access
Sometimes connection thread was running after command thread in OpenWebCommanderImpl (around line 130) => so the connection wasn't already open and so command was not executed (the connection thread was waiting command executed...)...
So now, when connection is required, I wait 20 millisecond before running the command thread to be sure the connection thread is launched (and lock the resource)....
Improve the heat image: depending the temperature the image is different.