Rename "primitive" to "mode".
Rename "primitive" to "mode".

There's a property named "primitive" in "mesh/primitive". This can lead
to confusion. Rename it to "mode" as it is called in glDrawArrays etc.

cyrillef/FBX-glTF,cyrillef/FBX-glTF,cyrillef/FBX-glTF,cyrillef/FBX-glTF