add lcov to ThirdParty and simplify coverage generation

.gitignore

CMakeLists.txt

ThirdParty/lcov/.version

ThirdParty/lcov/CHANGES

ThirdParty/lcov/CONTRIBUTING

ThirdParty/lcov/COPYING

ThirdParty/lcov/Makefile

ThirdParty/lcov/README

ThirdParty/lcov/bin/copy_dates.sh

ThirdParty/lcov/bin/gendesc

ThirdParty/lcov/bin/genhtml

ThirdParty/lcov/bin/geninfo

ThirdParty/lcov/bin/genpng

ThirdParty/lcov/bin/get_changes.sh

ThirdParty/lcov/bin/get_version.sh

ThirdParty/lcov/bin/install.sh

ThirdParty/lcov/bin/lcov

ThirdParty/lcov/bin/updateversion.pl

ThirdParty/lcov/example/Makefile

ThirdParty/lcov/example/README