I agree that it is very useful, but currently the only person who has access to this information is splash admin. It is fine when you run splash locally, but when using a shared splash instance this could become an issue.

In order to return this information to user we may have to change default render.js output format (e.g. to return json data with the result of computations and logs). So handling js logs can cause breaking interface changes - what about deciding something in this PR to have less breaking changes in master?