Initial version of libgames-scores

Fake pull request for initial review of libgames-scores.
       /* We need to check for game_window to be not null because thats a way to identify if add_score is being called by the test file.
        If it's being called by test file, then the dialog wouldn't be run and hence player name wouldn't be updated. So, in that case,
        we wish to save scores to file right now itself rather than waiting for a call to update_score.*/

I hope this made some sense for the need of the condition window != null