CSV files download should be async

[manumoreira]

In the last years CSV download has been generating several problems to the users. On medium to big surveys it ends up crashing the server frequently. A solution for this problem can be uncoupling file creation from download. This will imply a change in the user interaction. Initially the user will click to create the file, the creation will be processed and once it is ready the user will be see a button to download it. We will need mockups for this

(source)

Questions:

• Will it be usefull to have an option to trigger the file creation for all the files of the survey?

[matiasgarciaisaia]

Let's note that the file which usually gives issues is the Interactions file (I don't remember having had issues with any other CSV file - but please correct me, @manumoreira).

But it may make a lot of sense to share the same approach between different files.

We could also generate the task (to create the files) and then notifiy the requester via email.

[manumoreira]

In some cases we've seen issues with the results file in large surveys. I'd prefer not to add an email service for this, just to keep it simple. A circular progress bar might be enough.