Showcase: GUI for nmqtt_pub

[ThomasTJdev]

This is just a showcase for a GUI for nmqtt_pub. When the verbose parameter in nmqtt_pub is updated, the output will be much better. Furthermore, a config for previous connection or favorites could be generated for ease of connecting in the GUI (this will not happen in nmqtt library).

https://github.com/ThomasTJdev/nmqttgui

[python36]

@ThomasTJdev Thanks! I've updated the README #53 and added a link to your repository in the new GUI section. Closing this now. Great work!