Importing files with same layer names combines the collections

[tsvilans]

Describe the bug
Importing different .3dm files with the same layer names (i.e. different versions of the same model) assigns the objects to the already-imported Collections instead of making unique ones under the new file-level collection.

To Reproduce

1. Import 2 Rhino files with the same layer structure.
2. See error

Expected behavior
Collections corresponding to Rhino layers should be unique to each imported Rhino file.

Desktop (please complete the following information):

• OS: Windows
• Blender 2.80