More changes on error unification

[angiehjort]

Please make it so that i can bind some UI strings to the error messages, i need errors to have unique ID and message should be informative, details should contain details and not the message

for example, now:

{
  "name": "WaffleServerError",
  "message": "WS error",
  "details": "No versions were found for the given dataset",
. . .

would like it to be

{
  "name": "WaffleServerError/NoVersionsFound",
  "message": "WS error: No versions were found for the given dataset",
  "details": {dataset: "open-numbers%2Fddf--gapminder--population%23develop"},
. . .