bad4685988
Merge in CGD/gather-and-defend from dev/unitUpgradeIntegration to main * commit 'b0c3bf5ba1216d3aa7539cf73584c6915bac6fa6': Add Scorpion unit; balance ranged units; balanced level13 added level 13 Integration of upgrades for melee, ranged and house units; Lots of balancing and created levels 8 to 12; Added desert sprites and change background dynamicaly; Fix upgrade error when only 1-2 upgrades are put in a unit; Made it so that resources are collected automaticaly after a delay; Units need to be upgraded to access the better units now; Some visual updates on units; Added slinger unit (temporary graphics)