Background alpha support and interaction fixes

This update adds support for background alpha on export and resolves various interaction issues.

Changes

• Added support for background alpha on export.
• Fix: Undo/redo interaction when object is removed/added.
• Fix: Panning on playmode black blocked in horizontal.
• Fix: Issue with default quality modifier on exports.
• Fix: History for spring parameters and hover for objects panel.
• Fix: Issue with empty-object interactions.
• Fix: Selection box with dragging not working properly.