Add basic scene graph example.
Add basic scene graph example.

This actually demonstrates an issue in the
current scene graph code. The sn1 node
should not be yawing about the x/z plane.

QuLogic/vispy,julienr/vispy,sbtlaarzc/vispy,michaelaye/vispy,hronoses/vispy,bollu/vispy,sh4wn/vispy,julienr/vispy,inclement/vispy,dchilds7/Deysha-Star-Formation,QuLogic/vispy,inclement/vispy,srinathv/vispy,QuLogic/vispy,ghisvail/vispy,drufat/vispy,jdreaver/vispy,jay3sh/vispy,bollu/vispy,ghisvail/vispy,sh4wn/vispy,drufat/vispy,drufat/vispy,RebeccaWPerry/vispy,jdreaver/vispy,srinathv/vispy,Eric89GXL/vispy,inclement/vispy,Eric89GXL/vispy,Eric89GXL/vispy,sh4wn/vispy,michaelaye/vispy,kkuunnddaannkk/vispy,dchilds7/Deysha-Star-Formation,hronoses/vispy,sbtlaarzc/vispy,RebeccaWPerry/vispy,hronoses/vispy,jay3sh/vispy,ghisvail/vispy,michaelaye/vispy,kkuunnddaannkk/vispy,jay3sh/vispy,bollu/vispy,dchilds7/Deysha-Star-Formation,jdreaver/vispy,julienr/vispy,srinathv/vispy,sbtlaarzc/vispy,kkuunnddaannkk/vispy,RebeccaWPerry/vispy