Better solution for making a coverage badge

We had a simple script for calculating the coverage which was made available for coverage badge used in our README.md

After moving to a multiple project structure, this script has been hacked to able to work: !80 (comment 211287445)

We should try to find a better solution on how to solve this, so whenever we would be adding a new project to this repository, it should be picked up by the coverage calculation and hopefully don't need to think about changing any scripts or anything the alike.