UI/libobs: Undo/Redo Sources and Scenes

Implements the Undo/Redo for scenes and sources, ranging from renaming,
deletion, addition. It also adds several elements to libobs that were
designed to facilitate undo/redo, and should not affect the rest of
libobs.
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f