Blender Git Loki

-> Extension Node attribute support for FLT I/O

Extension node attributes are now read and stored as ID
props for the following Node types:

-Object Nodes
-Group Nodes
-LOD Nodes
-DOF Nodes
-Inline Light Point Nodes


The extension data is written back out on export.

Note that this commit only adds support for attribute extensions.
Completely new node types via the extension record are still
unsupported.