- proper gitignore.
- update material previews when textures pertaining to a material have either finished loading or are replaced by user action.
- MaterialThumbnailControl: fix race condition in UpdateMaterial(), add error image.
- SceneRendererClassicGl: use second rendering pass to draw transparent draw jobs.
- SceneRendererClassicGl, MaterialMapper: consistent handling of semi-transparent materials.
Merge branch 'master' of github.com:acgessler/open3mod

Conflicts:
	.gitignore