Code coverage visualization & Gating

[dkrupp]

Basic Visualization of coverage data
Test Code coverage is an important quality metric of a project similarly to static analysis results.
It should be possible to visualize the test coverage for each file line by line to understand which part of the code is covered.
It should be possible display the overal test coverage by mean of % line of code covered.
It should be possible ot display the test coverage on a directory aggregated level.

Diff & Gating
It should be possible to detect whether the coverage descreases for the new code version.
It should be possible to configure coverage descrease as a gating step (to prevent submitting code with decreasing coverage).

Supported coverage formats
Supported coverage fromats should be supported:
https://gcc.gnu.org/onlinedocs/gcc/Gcov.html
https://github.com/jacoco/jacoco