Hull upgrade rework

[BiffW]

Issue with current hull upgrade

In current state, the hull upgrade increases the max health of shell directly which can lead to an issue that it takes more time to repair the upgraded hull. For example: If you fight some creature that does 1000 structure damage in one hit, 200 max health is actually the same as 1000 max health. In this case, the latter takes 400% more time to fix which is more a downgrade than upgrade.

How to rework

Implement a damage resistance for structures. When player upgrade their hull, increase the damage resistance instead of increasing the max health. The damage resistance should reduce positive structure damage while not affacting negative structure damage.