Dockerfile for mqtt-server & dev_env integration
removed logs dir from .gitignore
removed client.js from mqtt_server

* was a (now useless) dummy
better dir structure for mqtt_server
new dir structure for distribution and data-utils

* changed dir structure to fit more to conventions
* moved helper functions into own module: data-utils
Modularised dev_env with new tests

* mqtt server in container
(docker related) linked mqttServer & sensorDB