web_renderjs_ui: make error page a bit more readable

  - indent the json representation of error
  - if error is an XMLHttpRequest:
    - include the server side error response in an iframe
    - split response headers
5 jobs for feat/renderjs_server_side_errors in 0 seconds
Status Job ID Name Coverage
  External
failed ERP5.UnitTest-TestRunner2

03:10:50

failed ERP5.UnitTest-TestRunner2

02:38:11

canceled ERP5.UnitTest-TestRunner2

13:46:39

failed ERP5.UnitTest-TestRunner2

08:57:04

canceled ERP5.UnitTest-TestRunner2