Automatically generate coverage reports

[ghost91-]

Summary

We should regularly (triggered by ci-builds) generate coverage reports. The total coverage should be displayed in the README.md as a badge.

User story

As a developer, I want to see the total coverage in the README.md so that I have quick access to this information.

Rationale

Having regular coverage reports will animate the developers to ensure that coverage increases. #1 also states that we are aiming for a coverage of at least 70% and this feature will enable us to see, if we hit or miss that goal.

Acceptance criteria

• generate coverage reports on every ci-build
• use https://codecov.io to analyze and display the coverage information
• display a badge showing the total coverage in the README.md

[pheerai]

This is implemented with #28