Convert the inventory screen (and all InventoryOperationsScreen screens) to NUI

[BenjaminAmos]

Description

This pull request converts the in-game inventory screen to use NUI. It should function almost identically to before, however it may look a bit different. Any UI design critiques would be appreciated.

Testing

• This pull request affects all screens that use the inventory's functionality.
• The following screens are affected and should be double-checked against an older build to identify possible regressions:
  • TutorialManager
  • BuyItemsScreen
  • SellItemsScreen
  • ChangeShipScreen
  • ChooseMercenaryScreen
  • GiveItemsScreen (give items to a mercenary)
  • HireShipsScreen
  • ShowInventory (the "Items" screen)
  • TakeItems (take items from a mercenary)
• As a guide, at least the following things should be checked:
  • Is the appearence similar to before (or better)?
  • Do all of the key-bindings work as before?
  • Does the screen function the same as before (or better)?
  • Can you buy items? Does it cost you to do so?
  • Can you sell items? Do you profit from doing so?
  • Can you hire mercenaries? Will they follow you afterwards?
  • Can you change ship? Will it cost you to do so? Does your ship actually change?

Notes

• This supersedes NUI inventory screen #636.
• This depends on New NUI widgets (EmptyIfInvisibleContainer, UIBackingBox and UILabelledIcon) #664, Convert remaining MainGameScreen visuals to NUI #665 and Convert the talk screen to NUI #667.
• Until the dependant PRs are merged, it might be easier to view the changes made in this pull request by viewing the diff between this one and the talk screen PR at BenjaminAmos/DestinationSol@nui-screen-conversion/talk-screen...nui-screen-conversion/inventory-screen.