Battle Brothers v0.6.0.21

Added new swamp combat environment. Added new mountainous combat environment. Added new snowy forest combat environment. Added new hilly combat environments for grassland, tundra, steppe and snow. Changed 'Swipe' scenario to use the new forest environment. Changed 'Early Game' scenario to use the new swamp environment. Fixed mountains, snowy forests and shores on the worldmap not being linked correctly to their combat environments. Requires starting a new campaign to take effect.