Colored mesh resource markers

These changes allow for tinted mesh resource markers, if mesh_use_embedded_materials is true and the marker color is anything other than r = 0, g = 0, b = 0, a = 0, as specified here: http://www.ros.org/wiki/rviz/DisplayTypes/Marker#Mesh_Resource_.28MESH_RESOURCE.3D10.29_.5B1.1.2B-.5D.