Check file after upload

[MichaelRoeder]

User Story

As a user, I may have generated a file that has some issue. At the moment, GERBIL only tells me that it failed to parse my file 1) without a detailed error message and 2) after the experiment is done. It would be better if the file would be checked directly when it has been uploaded.

Solution

• Let the file upload execute the loading of the data.
• If the loading fails, a detailed error message should be printed.
• In case of success, the file upload could answer with "n documents loaded" or "n questions loaded".