Barbarian units

[SimonCeder]

• Enables the unique Barbarian units that were commented out in Units.json, with the exception of the barbarian Swordsman since the stats are identical anyway. To avoid name collisions, the archer is renamed "skirmisher" and the spearman "marauder". I've made slight edits to the pixel sprites to give them a visual distinction, but I'm sure that other people will improve on that later.
• Allows the barbarians to spawn units that require strategic resources such as Horsemen and Swordsmen.
• Introduces a blacklisting unique that forbids the barbarians from spawning certain units, barbarians will never again spawn Scouts or Submarines.

Also, because I observed that some civs still get stuck without being able to expand on Raging Barbarians, I modified afraidOfBarbarians to allow civs to keep building up units for a bit longer if they haven't been able to expand.