Correct fix for issue #75

[cornelcristea]

Summary:

1. It was observed that fix for issue Part of the left menu will turn white after opening the option #75 was done in Dark.qss file but this file is generated based on Dark.scss source file each time when theme is built. Fix was added on source file.
2. For build process, the qtsass tool was called from author local storage and the contributors do not have access on this path. Build script were updated to install qtsass python library using pip command and requirements.txt file
3. Small updates for build scripts (python keyword for scripts, commands indentation, remove useless step)
4. Minor correction for make-resource.py script

@jagannatharjun could you review my changes, please ?

Thank you!