280: Set LOD for Collections 1-4 during update from Root Exports

[tngreene]

If you were using Root Objects mode in 2.79, you were using Layers 1-4 as buckets 1-4.

The "Widths" of the buckets will still be on the root object, the contents of those buckets will not be in collections 1 through 4.

If #451 is to be implemented, Collections 1 through 4 will have to be marked with check boxes 1 through 4.

This report is still a WIP and will change on what happens with #451