Convert TutorialScreen to NUI

[BenjaminAmos]

Description

This pull request re-implements the tutorial UI using NUI. Since the tutorial interacts with most of the in-game UIs, this relies on the majority of other in-game UIs being converted to NUI first.

Testing

• Start the game and select "Tutorial" from the main menu.
• Follow the instructions in the tutorial. Every step in the tutorial should function as explained.
• Try using alternate methods for doing things in the tutorial, such as opening screens via the mouse or using keyboard shortcuts.
• Ensure that the tutorial text is never cut-off.
• The tutorial text box should not completely cover important UI elements.

Notes

• This pull request depends on General NUI Fixes #663, New NUI widgets (EmptyIfInvisibleContainer, UIBackingBox and UILabelledIcon) #664, Convert remaining MainGameScreen visuals to NUI #665, Convert the talk screen to NUI #667, Convert the inventory screen (and all InventoryOperationsScreen screens) to NUI #668 and Convert MapScreen and WaypointCreationScreen to NUI #669.
• The only new commit in this pull request is ce4c8e3.