Change defaults for data sets iframe src

This change was requested by Daniel from Sheffield:

We have updated our servers to the latest version of the code.
Unfortunately, this means you need to update your iframe.
The new location is: https://eurvalve.sheffield.ac.uk/WebQuery/site.html?dataset=XXX&access_token=YYY
Let us know if there is any problem.
Sorry for the inconvenience,

This was already changed on production using env variables, but it would be good to keep correct defaults also in default configuration.