Adds GSStoryPage::IsValidStoryPageButtonColour, GSStoryPage::IsValidStoryPageButtonFlags and GSStoryPage::IsValidStoryPageButtonCursor to the API.
Add missing enforced preconditions to validate parameters passed to MakePushButtonReference, MakeTileButtonReference and MakeVehicleButtonReference.
Fixes a crash that happens if an invalid StoryPageElementType is passed to ScriptStoryPage::NewElement.
Adds an enforced precondition that tests the validity of StoryPageElementType.
Adds GSStoryPage::IsValidStoryPageElementType to the API.
Direct 1:1 replacements in the code, and comments now refer to either
GSCompanyMode::IsValid or GSCompanyMode::IsDeity instead of several variations
on "company mode active" or "no company mode active".
Allow more direct player-initiated interaction for Game Scripts, by letting the GS put push-buttons on storybook pages. These buttons can either trigger an immediate event, or require the player to first select a tile on the map, or a vehicle.
Additionally this reworks how the storybook pages are layouted and rendered, to allow for slightly more complex layouts, and maybe speeding drawing up a bit.