Fix the "Exception 0" in Studio

Fix the "Exception 0" in Studio, which makes some tests fail. Should we put in place some kind of big try/catch and/or logging to get useful traces for such problems

• issue seems to be that request is aborted because of page reload. GWT internals are receiving a request object with Status 0, following the onreadystatechange event. GWT internals only accept 200 OK => raise exception. By improving response time we might not encounter the issue any more. But this is not a 100% safe solution, and even if we get sometimes popup for such exception, it is pretty bad for user experience
• see git commits to revert
  • 2d29e3f006b8b768cc861cce2d13b38929ac47a1
  • 4137dcb9a33397c8cb5ed99beb982518a13c8b19

The work on the counter of requests and cancelling (see linked issue), should solve the problem. If so, this task should only consist in reverting the changes indicated above.