Page rendering is slow (does not properly render until JSMol is loaded)

Probably we should make sure the JSmol rendering is delayed (maybe it's enough to move this into the onload method?)

EDIT: I checked, it's not as trivial - moving the loading of JSMol in the onload function does not work (the widget does not appear and there is a mysterious JQuery error in the console).

(Moved from giovannipizzi/seekpath#63)