Issue 639 - Federation group support

[carmenfan]

This fixes #639

Description

This issue is to change the federation scene graph to match what we have proposed in 3drepo/3drepo.io#4391:

• Removed the parent transformation before a ref node (it's always an identity matrix due to the way we create federation)
• Instead, take in a set of reference nodes and its group name (if any)
• turn group name into parenting transformation nodes, if there is none, wire the ref node to the root node.

Test cases

• Should continue to produce working federations
• Should be able to create groupings to group submodels under the same branch
• Submodel references should be wired to the root node they do not belong in a grouping.