Sector map changes in size + balance improvements! + more!

1. New: map sector size changes depending on its danger level: lower danger means smaller area, higher danger means bigger area.
2. Improved: the sectors with lower danger levels have more resources so there is a better incentive to explore them.
3. Improved: balanced the enemy wave creation to make the combat more fun.
4. Improved: balanced the amount of "bullet shooting mini-bosses" that can appear in a sector, now they are fewer depending on the danger level, sometimes they where too many and it was impossible to survive.
5. Improved: changed the shape of the "target move position" of the explorer, now it looks a bit more tridimensional.
6. Improved: new UI of the "danger level" and "resources quantity" on the "sector exploration screen" at the top left, now they have different horizontal bars.
7. Improved: new market prices.
8. Fixed: the shadow of the explorer was showing on top of him, now its below him.
9. Fixed: the area of collision detection of the explorer was too big, now its smaller so its easier to evade enemy attacks.
10. Fixed: trying to move close to the explorer was not possible because his sprite was blocking clicks on the floor.
11. Fixed: employees inventories where not being saved properly when you changed screens. Now all their stats and numbers will be updated correctly if you switch screens and also when you quit and enter the game.
12. Fixed: when the explorer entered and exited the robot there was an error, not anymore.
13. Fixed: sometimes it was impossible for the explorer to use the ladder to get into the robot.
14. Fixed: when you collected all the resources of a sector, the sprite indicating the completion percentage was showing in the wrong position.
15. Fixed: when the explorer destroyed an object to extract its resources, the resources UI bar was not updating.
16. Fixed: saving items to build was not working correctly.