function mxVsdxMaster(m, model) {
                        /**
                         * Unique ID of the element within its parent element
                         */
                        this.Id = null;
                        this.masterShape = null;
                        this.childShapes = ({});
                        this.master = null;
                        this.master = m;
                        this.Id = m.getAttribute(com.mxgraph.io.vsdx.mxVsdxConstants.ID) || "";
                        this.processMasterShapes(model);
                    }
Create a new instance of mxMasterElement and retrieves all the shapes contained
in the Master element.
@param {*} m Master Element to be wrapped.
@param {com.mxgraph.io.vsdx.mxVsdxModel} model
@class