Store ci artifacts
Closes foodsharing-dev/issues0#26 Closes foodsharing-dev/issues0#253
What does this MR do?
- links the selenium downloads into the test/_output folder
- stores test/_output (including downloaded files) as test artifacts.
How confident are you it won't break things if deployed?
Links to related issues
- added a test, or explain why one is not needed/possible...
- no unrelated changes
- asked someone for a code review
- joined #foodsharing-beta channel at https://slackin.yunity.org
- added an entry to CHANGELOG.md (description, merge request link, username(s))