public final ObservableList<ToolbarItem> getToolbarControlsLeft() {
        return toolbarControlsLeft;
    }
Returns an {@link ObservableList} which stores the toolbar items of the module.
If it's not empty, the {@link Workbench} creates a pre styled {@link ToolbarControl}
and adds the stored items on its left side.

@return the {@link ObservableList} of items which are displayed on the left side of the
automatically added {@link ToolbarControl}
workbenchfx-core/src/main/java/com/dlsc/workbenchfx/model/WorkbenchModule.java