[ROTKR-79] Rats can be healed

[hatfield-c]

There is no way for rats to be healed at this point in time.

I do not think it would be wise to have scrap heal rats at the chop shop, as then the player is will likely always choose to heal the rats instead of repair the ship.

There should be some way for the rats to regain health. Suggestions include:

• Small health gain after every completed Wye
  • High difficulties get less of a gain
• Item drops from enemy ships that regain health