Feature/lcov remove extra

Add support for variable `LCOV_REMOVE_EXTRA` which can be set before calling `setup_target_for_coverage()` to add additional arguments to `lcov --remove`.

Example usage in CMakeLists.txt:
```cmake
# remove thirdpaty/* sources from lcov report
set(LCOV_REMOVE_EXTRA "'thirdparty/*'")
setup_target_for_coverage(test-${projectName}-coverage test-${projectName} coverage)
```