Exists there a 3D model designer which as easy to use as SH3D?

Short answer, no - see this thread and lots of other threads.

AoI, Blender, Sketchup, Wings 3D - and then obviously commercial ones - matter of preference. All 3D modelling software will require some patience in the learning process.

Furniture Library Editor: Just a "converter"..

The Furniture Library Editor is a furniture library editor [:-)] it deals with libraries of models: converts, scales, lets you add cut-outs etc. but not designer.

Note that for the door swing you wish to display in the 2D win, you need only an editor - PluginFurnitureCatalog.properties is a (zipped) plain vanilla ascii file specifying properties of library elements.

ok