Make XKTLoaderPlugin load most colors from model by default

[xeolabs]

Make XKTLoaderPlugin load colors from most IFC types in the model, except for certain types, which for convenience often need to be forced hidden or transparent.

IFCObjectDefaults, which is the default value for XKTLoaderPlugin#objectDefaults is now as below.

const IFCObjectDefaults = {

    IfcOpeningElement: {
        pickable: false,
        visible: false
    },

    IfcSpace: {
        colorize: [0.137255, 0.403922, 0.870588],
        pickable: false,
        visible: false,
        opacity: 0.5
    },

    IfcWindow: {
        colorize: [0.137255, 0.403922, 0.870588],
        pickable: true,
        opacity: 0.1
    },

    IfcPlate: {
        colorize: [0.8470588235, 0.427450980392, 0, 0.5],
        opacity: 0.3
    },

    DEFAULT: {
    }
};

This change also adds IFCObjectDefaultColors, which has the original properties of IFCObjectDefaults. Use that map when you want to apply IFC color codes to your objects.