Creating new subasset doesn't add a child widget item

[zhaladshar]

When creating a new asset and marking it as a subasset, the asset widget tree will not create a child item but will add a top level item instead.

[zhaladshar]

This was caused by having the addTopLevelItem method in the main part of the asset creation code rather than indented into the branch for adding non-subassets.

This has been indented inward and the routine for adding a child item moved into the subasset branch.