Update binary JData output format to match BJData spec Draft 2

[fangq]

The recently released BJData draft 2 changed default endian type from Big-Endian to Little-Endian. The UBJ C library was also updated to reflect such change.

It is necessary to update the bundled ubj source code in mcx to output Draft-2 compliant .bnii file.

Also see mailing list bug report: https://groups.google.com/g/mcx-users/c/c9mPMjd0RQw