Measure code coverage

[bjoern-arnold]

As a developer I want to have an overview of the code lines / branches covered by the tests executed during the build process.

Proposed solution approach:

• Include Jacoco plugin in backend build process.
• Include babel-plugin-istanbul in frontend build process.

In order to reduce the impact on the build duration, the code instrumentation may be integrated as an optional step that can be activated on demand, e.g. via a build profile or configuration setting.