Make import of Joint node hierarchies less strict

This is a fix for the commit: 1a336bb39eb029966790219d8942169905e39132

The above mentioned commit assumes that nodes of type joint always have an associated sid.
However i could not find any hint that sid is a required attribute for JOINT nodes.
Furthermore the "FBX COLLADA exporter" creates node hierarchies without sid's. 
It uses the id attribute instead.

I prefer if the OpenCollada library is more tolerant to Collada files, 
especially this particular case can be nicely auto fixed, 
since i believe that we safely can use the attribue id 
here as scoped id when no sid is specified.

note: I am not sure if the last fallback (use attributeData.name as node sid) is a good idea, so this last fallback can also be removed again if it doesnt make sense here.