#2350: Generate survey files async

[anaPerezGhiglia]

Changes

• create new SurveyResults GenServer
• move responsibility of generating files from RespondentController to new SurveyResults actor
• change files endpoints to "common" POST (without csv format)
• change UI to make the POST call instead of a redirect to a new location

Out of scope

• Keep track of generated files in the db
• Files cleanup policy
• Download existing files

for #2350

[matiasgarciaisaia]

First of all, sorry for the huge PR. Things got wild.

Here's my list of pending things, which we may want to move to a different issue/PR.

• [x] Bug: not sending the filter to the file status request
• [ ] Improve downloads modal UX (prevent generating a file that's being generated, show the user a file is currently being generated, add an exponential backoff to check the files status after triggering a file generation)
• [ ] Filtered results files should consider the filter (ie, don't show a disposition:completed file if filtering for disposition:ready).
• [ ] Check Survey state against pre-generated files (eg, don't offer to download a file from when the survey was running if it's already finished, maybe prevent regenerating files from finished surveys)
• [ ] Only return status of files that the user can access (we're leaking some harmless info there - files can't be downloaded by unauthorized users)
• [ ] Avoid concurrent fetchRespondentsFilesStatus calls
• [x] Fix skipped tests

I'll try to address some of these while we review the PR.