Usage of DelegateModel for model filtering has not proven to be the most stable solution, and might be responsible for random crashes happening during engine's garbage collection. Implement Loader-based alternative:
* first delegate is a Loader which creates the AttributeItemDelegate if necessary
* compensate spacing using negative height when element is hidden
* allow to solo a 3D media from the GraphEditor by double clicking on a node or an attribute with the Control modifier pressed
* consistent with Viewer3D.MediaLibrary behavior (solo on Ctrl+Click on visibility button)
* handle supported file extensions in Viewer3DSettings
* NodeEditor
* exposes Node parameters: compatibility, attributes and logs
* provides a placeholder when no active Node
* AttributeEditor
* only displays the list of Attributes
* use 'AttributeEditor' for GroupAttributes in AttributeItemDelegate
* Layout
* move NodeEditor on the same SplitView level as GraphEditor
* move current node name and menu to the Panel's header
* bugfix: in latest PySide2 versions, application palette is not properly applied to all QtQuick Controls 2 components. Force this by exposing QApplication palette and bind it to the root ApplicationWindow.
* rename all "palette" ids to "activePalette" to avoid clashes with "palette" property on QtQuick Controls 2
* use parent component palette when it makes sense to propagate active/disabled style (instead of always using Active SystemPalette)
* avoid duplication of code for displaying labels of GroupAttribute's children
* display input/output aligned to the left/right
* add a background to improve readability
* give access to Node's chunks log files (log, statistics, status) with auto-reload when current NodeChunk is being computed
* add tabs system in the AttributeEditor to switch between attributes edition and Node log
