Update hdMoonray to bind to named outputs #302

hdMoonray needs to be updated to allow binding to named outputs. hdMoonray: lib/hydramoonray/shader_utils.cc has a function getTerminalInternal which sets up all of the bindings by iterating over a list of HdMaterialRelationship objects. Currently the inputName is ignored which would be the name of output on the shader being bound to.

The MoonrayAttribute::set() function and ValueConverter::setBinding() function will need to be updated to accept an output name so that it can be passed on to SceneObject::setBinding