#1124 Export objects to SH3F from the 2D plan

[shoulders]

This is a must because currently you can only export as an OBJ which strips all of the extra information that Sweet Home 3D adds. This will be in addition to export as OBJ.

Exporting from the library by right clicking is also useful if easy to add at the same time which would save having to add the item to the plan before you could export it. this is not as important though.