[feature request] missing some good stuff about assemblies

Back when issue #218 was still open, I had a workaround so I could see assemblies in cq-editor and avoid that crash:
```python
for key, val in asy.traverse():
shapes = val.shapes
if shapes != []:
c = cq.Compound.makeCompound(shapes)
odict = {}
if val.color is not None:
co = val.color.wrapped.GetRGB()
rgb = (co.Red(), co.Green(), co.Blue())
odict['color'] = rgb
show_object(c.locate(val.loc), name=val.name, options=odict)
```
Now after #238 I can just do: `show_object(asy)` and my parts show up in the CQ-editor window with no crashes, yay!

However, with my workaround/hack to solve the problem, the subassembly pieces were individual parts in the CQ model/object tree so I could show/hide them independently and they knew the names I gave them in my code which was quite convenient:

But after PR #238, the assembly seems to be combined into one object with a mysterious name:
I think combining things in the object tree hides some of the power of assemblies.

Ideally, I think the CQ object pane would be a hierarchical tree view where you could expand/collapse multilevel subassemblies (if that's even a thing) and hide/show whole assemblies or just one piece or subassembly with the check boxes as you wish, but I think that work isn't really worth it, and just flattening the tree and listing all the subassembly pieces with their names and would be 90% as good.