Fixes for the collada exporter.
- resetting bones after each action export -> important if actions miss keyframes for certain bones
- resetting object transformations. It can happen when animations are exported that objects are moved afterwards.
- restore the same object selection as before the export
- fixed image export for packed images. before the exporter has thrown an error because the image was not found from the resource folder. If file is packed the exporter saves it now directly from blender as a .png file

As far as I can tell there are no obvious errors currently. Tested with a few testscenes and imported them into godot.