Fix interleaving offsets and stride not getting inherited

Nodes inheriting VBOs from other nodes need to get the correct
interleaving parameters from them as well to render the geometry
correctly. Fixes regression from commit "Interleave vertex attributes
into a single buffer for more efficient drawing". Tested by
examples/geometry/vertexSharing.html.
Merge pull request #315 from NVIDIA/fix-vertex-sharing

Fix interleaving offsets and stride not getting inherited
Cube mapping support - added new "cubemap" node
Task status popups enabled by default
Cube map environment reflection example
Rebuild library
New plugins: "cubemaps/london" and "cubemaps/clouds"
Plugins and ZIPs rebuild
Merge branch 'V3.1' of https://github.com/xeolabs/scenejs into V3.1
Tweaked cubemap example
Cube map environment reflection example tweaks
Cube map environment reflection example #2
Typo fix in example index
Fix shader texture unit clash between 'cubemap' and 'texture' nodes
Try environment map on a physics demo
Environment map on physics demo
Remove environment map from physics demo
Built new ZIP
Example of environment map on .MD2 mesh
Tweaked cube map environment reflection example