Create mouse down events

adds an atom picked event to be sent to the dom element.

This can allow highlighting of selected residue etc from the application. 

This is some example code to show how to access the events

<code>var callback = function(e) {
    e.preventDefault();    
    console.log(" Atom number=" + e.detail.atom.residue().num());
};
viewer._domElement.addEventListener("atomSelected", callback, false);
</code>