Display an upload/update counter/timer

[aaaaalbert]

It would be great to have some kind of confirmation for Sensorium uploaders that their data arrived at our server. It need not be too specific, I think a simple "Last upload" plus timestamp (according to the browser's locale) would suffice.

On a similar token, it's pretty unclear right now when updates/recalculation of cell etc. data happen. A potential fix would be to just display this information as a timestamp in, e.g., the Cell view tab.