- correct all icon usage. use 'CANCEL' instead of 'ERROR' to indicate error correctly. and move these icon const into UTILS_icons_manager.py
- auto rename generated rail section to match the default name standard.
- give more clear signal about import and export bm file by using Operator.report() function.
- add support of 4 alpha fields intorduced in BM spec recently.
- optimize material creation functions argv passing strategy.
- change related func calls of (2).
- optimize material parameter pick code to reduce useless check.
- split blender material creation function.
- allow user to apply virtools material to blender nodes in operator.
- add quick group picker in add virtools group operator.
