## Asset Package References
* Added **ezDependencyFlags** which defines how a reference in an asset is used:
  *  **Thumbnail**: This reference is a dependency to generating a thumbnail.
  *  **Transform**: This reference is a dependency to transforming this asset.
  *  **Package**: This reference is needs to be packaged as it is used at runtime by this asset.
* **ezAssetBrowserAttribute** now has a new parameter to set the `ezDependencyFlags` for it. By default, **ezDependencyFlags::Thumbnail | ezDependencyFlags::Package** is set.
* Fixed naming of various enums and member variables to match the new `transform`, `thumbnail` and `package` dependency naming pattern.

## Circular Dependencies
* Circular dependencies will no longer deadlock the editor and instead result in a new error code on one of the assets in the circle: **ezAssetInfo::TransformState::CircularDependency**.
* **ezAssetCurator::GenerateTransitiveHull** is no longer recursive and can handle circular dependencies.
* Added **ezAssetCurator::GenerateInverseTransitiveHull** which generates a set of all assets that depend in the given asset. Used by the new **ezAssetCurator::CheckForCircularDependencies** function.
* **ezAssetCurator::InvalidateAssetTransformState** is no longer recursive, using **GenerateInverseTransitiveHull** instead.
* **ezQtAssetPropertyWidget::InternalSetValue** will prevent the user now from creating circular dependencies.

## Misc
* Added **Asset.WriteDependencyDGML** action which creates a DGML file containing all transform and thumbnail dependencies this asset transitively depends on. Very useful to understand circular dependencies.
* Added **ezAssetActions::MapMenuActions** to put `Transform Asset` and `Write Dependency DGML` into the edit menu.
* **ezCollectionAssetDocument** are no longer updated automatically as their transitive naturure can't be tracked correctly by the currently defined `ezDependencyFlags`. Instead, they are set to manual transform and will be auto-generated on every scene export.