mipmapping for the cubemap tool added pmrem images

closes MaxDaten/yage#46
added Sea env cube map faces (now png) added cycling through envs

deletion of the bmp incoming
Merge branch 'feature/physically-based-rendering' of github.com:MaxDaten/yage-examples into feature/physically-based-rendering

Conflicts:
	src/YageCubeMapTool.hs