function createParcatsModel(dimensions, paths, count) {
    var maxCats = dimensions
        .map(function(d) {return d.categories.length;})
        .reduce(function(v1, v2) {return Math.max(v1, v2);});
    return {dimensions: dimensions, paths: paths, trace: undefined, maxCats: maxCats, count: count};
}
Create and new ParcatsModel object
@param {Array.<DimensionModel>} dimensions
@param {Object.<string,PathModel>} paths
@param {Number} count
@return {ParcatsModel}