Add an Option to Select a seed before starting a scenario with a random map

[Kodenith]

When entering scenario's with random maps, there's a good chance that the player may start off in a weird or difficult position, or start without important buildings due to the terrain. having an option to select the seed before starting the scenario would make it much easier to start off a scenario without having to worry about restarting 20 times because of the game generating a poor or unplayable map, as the player could have the perfect seed for them saved somewhere to use.