simplified light export
moved export menu item
implemented simple custom attributes menu and area light visibility flag
removed custom attribute code from MMsMaterial, and added it to MGenericMaterial
fixed custom attribute acquiring code for MGeberic  material
implemented front/back sample custom attribute
implemented importance multiplier and cast indirect diffuse custom attributes for area lights
added double shading custom attribute for materials
house keeping
house keeping
fixed potential naming conflict on export
added importance sample check box to config settings
removed code to set default value
house keeping
added environment render pass as default
implemented double sided shading custom attrib for auto translated materials
fixed output of secondary surface shaders
fixed a big that resulted in duplicate surface shaders
fixed misnamed parameter in displacement export
added parameter list to AsEnvironmentShader