Updated import options gui with tree view, additional shape statistics and settings load/save options. See /Engine/lib/assimp/t3d_usage.md for usage tips.
This commit deals with the problem that the keyframe timestamps are not standardized. Seconds, milliseconds and ticks are used depending on the import format. There is no metadata or property that specifies the format used, so the option is exposed to the user as part of the import options gui.
