Set icon for Mbaza that works in all places

[tadeuszbaraslupski]

Acceptance criteria

• new icon is displayed in the app, on the desktop shortcuts, in system bar
• works at least on Windows and Linux, and ideally also on Mac (paste screenshots to streamline code review)

More info

Documentation is here, but I think it's not exact https://www.electron.build/icons. Instead you may need to add all files as in the resources folder in https://github.com/electron-react-boilerplate/electron-react-boilerplate/tree/master/resources (I deleted most of them at some point because from the docs it seemed they were not necessary)

Final design approved by Robbie below.

JPG: https://drive.google.com/open?id=15e-1JaNTV89qiE2qwpp-oXbknief4Qtv
SVG: https://drive.google.com/file/d/1dS5pEkiijpPOzpuBtHzp94Z60UnstJ4U/view?usp=sharing