- add hint for gray virtools import export button
- add outcome of leaving blank ballance texture folder setting.
- update compile chapter according to the change of build scripts.
- move assets (raw jsons, icons, meshes and i18n data) into the root of repo.
- move script into the root of repo.
- modify blender manifest according to this changes.
- optimize gitignore.
- try setting center alignment for add floor popup operator. it is not center alignment now because blender's impl but it is better than previous layout.
- add some components icon for more directly visual.
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