Too many options for Euler angles rotation order

Currently, there are 12 options in front-end (Node.rotationOrder) and 24 options in back-end (qssgeulerangles).

These are too many to maintain especially considering conversion from/to common Qt types and functions. (Also, conversion functions in the back-end are very tricky ones.)

As it seems like most of the options are not used, it will be better to keep only a few necessary options and discard others to make it easier to maintain in the future.