New cmake-options:
- "-D WITH_COVERAGE=ON" to activate,
- "-D COVERAGE_EXCLUDES=/usr/;..." for filtering

Adds dependencies on:
- fastcov, gcov, genhtml
- Necessary Find*.cmake packages provided and conditionally activated

This option adds two consecutive test targets to each test:
- <test>_coverage
- <test>_html

Build:
- "ctest" to generate and run tests and generate html coverage report
- Then look for <test_bin_root>/html/index.html

Signed-off-by: Rene Paris <rene.paris@in-tech.com>
Signed-off-by: Reinhard Biegel <reinhard.biegel@in-tech.com>