Consider using CMake's FetchContent module

[traversaro]

Some of the logic related to downloading and unzipping the tarball could be probably be simplified by using CMake's FetchContent Module.

See robotology/gazebo-fmi#2 .

[S-Dafarra]

Thanks for the suggestion! To be honest I am not entirely sure how it should be used in this case. Would it change only the download part or also the build mechanism would be automatized?