Add bitmap backgrounds, legend3d, bgplot3d.  
Delete unused QuadSet.cpp file.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rgl@1145 79a1b648-8b68-254f-b20b-c0b50f5137bf
Documentation fixes:  add note about writeWebGL to bg3d, make spelling of color consistent.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rgl@1146 79a1b648-8b68-254f-b20b-c0b50f5137bf