Dates are saved in user's locale

[mslw]

Looking at a small subset of collected data I noticed that we have two date formats (e.g. for date-of-test), yyyy-mm-dd and dd.mm.yyyy. These seem to correlate with entry IP address. Although the mixed-format dates are still resolvable, this introduces unnecessary ambiguity into the raw data.

Looking at the code, this is probably because we use <input type="date"> and then getStringContent from that.