Converts the ad-hoc design of the Material Editor to utilize the same inspector interface as most everything else does.

- Overhauls the material editor to simplify and streamline the logic behind it since the inspector does most of the work
- Tweak a few order positions of materialdefinition fields to work better
- Sets AO, Rough and Metal channel fields to use an enum type for human readability
- Updates the MaterialPreview gui control to work with assetIds
- MatEd now supports setting of parent material to inherit from
- Creating a new material now can prompt selecting an existing material to inherit from
- Can now edit the mapTo value of a material in the matEd
- New standalone Composite Texture Editor window for convering AO, Roughness and Metalness maps in a material to an ORMMap
- Can also star the creation of a composite texture via RMB context menu in AB on an image asset
- Moved logic of CubemapEditor from MatEd to it's own stuff
- Made ImageAsset fields now be more clear when they have nothing assigned, and also have a clear button to empty the field's value so it's consistent across the board
- Reorganized the layout of the gui and image files for the MatEd to be easier to navigate
- MaterialEditor now overlays the EditorGUI instead of being forcefully embedded in it, allowing easy editing of the MatEd Gui via the Gui editor

Engine/source/T3D/assets/ImageAssetInspectors.h

@@ -16,7 +16,9 @@ public:
    GuiTextCtrl* mLabel = NULL;
    GuiBitmapButtonCtrl* mPreviewBorderButton = NULL;
    GuiBitmapCtrl* mPreviewImage = NULL;
-   GuiButtonCtrl* mEditButton = NULL;
+   GuiBitmapButtonCtrl* mEditButton = NULL;
+
+   bool mIsDeleteButtonVisible;
 
    DECLARE_CONOBJECT(GuiInspectorTypeImageAssetPtr);
    static void consoleInit();
@@ -29,6 +31,16 @@ public:
 
    void updatePreviewImage();
    void setPreviewImage(StringTableEntry assetId);
+
+   /// Sets this control's caption text, usually set within setInspectorField,
+      /// this is exposed in case someone wants to override the normal caption.
+   void setCaption(StringTableEntry caption) override;
+
+   void setIsDeleteBtnVisible(const bool& isVisible)
+   {
+      if (mEditButton)
+         mEditButton->setVisible(isVisible);
+   }
 };
 
 class GuiInspectorTypeImageAssetId : public GuiInspectorTypeImageAssetPtr