Make selection of imported objects optional

[vvoovv]

Is your feature request related to a problem? Please describe.

The glTF importer can be used for the import of thousands of glTF files one after another. Each subsequent import takes longer since it takes more time to deselect all objects that were imported before.

Describe the solution you'd like

Make selection of imported objects optional with a setting in the addon operator.

Describe alternatives you've considered

Currently I am patching the static method BlenderScene.select_imported_objects in the module io_scene_gltf2.blender.imp.scene. The method is set to an empty function.