Convert the talk screen to NUI

[BenjaminAmos]

Description

This pull request converts the Talk screen to NUI. It should functionally identically to before, although there may be some minor visual differences.

Before

After

Testing

• Start a new game (or continue an existing one)
• Fly towards the starting station until the Talk button is enabled
• Verify that the talk screen opens when you click on the Talk button
• Verify that each of the buttons on the talk screen behaves as before e.g.
  • Verify that the buy screen opens when you click on the Buy button (or press the B key)
  • Verify that the sell screen opens when you click on the Sell button (or press the S key)
  • Verify that the Change Ship screen opens when you click on the Change Ship button (or press the C key)
  • Verify that the Hire Ship screen opens when you click on the Hire button (or press the H key)
  • Verify that the talk screen closes when you click on its Close button (or press the Escape key)
• Test that this works for both the starting station and the stations found on planets

Notes

• This supersedes NUI talk screen #639.
• This depends on New NUI widgets (EmptyIfInvisibleContainer, UIBackingBox and UILabelledIcon) #664 and Convert remaining MainGameScreen visuals to NUI #665.
• Until New NUI widgets (EmptyIfInvisibleContainer, UIBackingBox and UILabelledIcon) #664 and Convert remaining MainGameScreen visuals to NUI #665 are merged, it might be easier to view the changes made in this pull request by viewing the diff between this and Convert remaining MainGameScreen visuals to NUI #665 at BenjaminAmos/DestinationSol@nui-screen-conversion/main-game-screen...nui-screen-conversion/talk-screen.