onebuild - packaging structure & python version upgrade

• Split 1build codebase from one single script to a module with multiple single responsible files
• Switch completely to python 3.5 & higher

Run 'before' and 'after' script/command – for regular commands in the project

• Support for before and after setup for each command
• Updated description
• pip install 1build==0.0.4
• Better logging messages
• Tests in place
• Readme images

Frictionless way of managing project-specific commands

• Install 1build from pip
• Run 1build with simple project file with commands