WEB: Split game downloads into a separate "Games" page

This separates binary ScummVM downloads from the freeware games and
extras downloads.

The current "downloads" page has become too crowded, and it contains both ScummVM binary downloads, plus freeware games and extras. Since it's hard to find out the games in that page, and since we will keep adding more freeware games in the future, it's best to separate the game downloads into a separate page