New Stars Status

A few more minor improvements, but they're the sorts of things that are important for playability:

• Implemented slot compatibility checks (no engines in weapon slots!)
  
• Implemented slot moving (used to have to discard and re-add)
• Implemented cost and design feature labels in ship designer
• Fixed a crash when the production window is not open, and a new design is created (tried to update the production list with the new design...)
• Improved zoom-in/zoom-out behavior (less shifting of the center point)
  

Here we can see the path highlighting I added last time. It also shows a ship with no engine being rejected. I also made the ship designer window a default size, which should reduce window resizing jitter. You can also see the cost/feature labels below the ship layout.