otherwise connections will be rendered in wrong positions in case of calling /positionGraph.

Conflicts:
	dream/platform/static/index.html
	dream/platform/static/src/dream_launcher.js

Also pass the the spreadsheet along the graph to the backend

fix convertToAbsolutePosition so that it works when a new element is added when the storage is empty.

* old
preference[element_id]['coordinate'] = {'top':..., 'left':...}
* new
preference['coordinates'][element_id] = {'top':..., 'left':...}