Rename VR headset transforms for different users

[dgmato]

In order to set up a collaborative VR session, VR headset transforms (HMD, left controller, and right controller) should have different names for server and client. If the name is the same, both server and client will be modifying the same transform node.

One possible solution would be to rename the VR headset transform during synchronization to differentiate the transforms from different users and avoid overlaps. Long node names should be avoided since a limited number of characters in the name is sent through OpenIGTLink.