Revert "Remove score-dialog that doesn't work, remaining score functionality should be working"

This reverts commit 3e08f33ba06145a7363ea7a6b9782c26dfc81062.

Conflicts:
	src/main.c
Revert "Remove more of the broken scores system"

This reverts commit 4bf47d434b4491b6641abddeccacede791e35813.
Bring up score dialog with multiple worms/game

Considering the min number of worms per game in two, I wonder what this
was ever about. There's a separate check below to make sure only one
human is playing.
Copy scores-backend.c and setgid-io.c from glines

For some reason we were stuck with a stub instead of a real copy of
games-scores-backend.