Update 1.2.39

Note: Updated data for vehicles won't apply to any unit that's already been spawned into a campaign, they will only affect newly spawned units.

FIX: Updated description and rarity factor for Churchill IV NA(75) FIX: If combat calendar is a single day long, it's now possible to get both the King and Queen of Spades Steam achievements on the same day FIX: Corrected rarity dates and updated BU visible zones for crew positions for Lee and Grant tanks (thanks PowderTrail!) FIX: Corrected rarity dates, armour values, and Loader BU visibility for the Jumbo Sherman (thanks PowderTrail!) FIX: Minor fixes for British/Commonwealth Shermans (thanks PowderTrail!) FIX: Improved crash handling when modded unit definitions are not formatted correctly in JSON