Closes #969: Removed fake path in message
Closes #1111: Possibility to download all submissions from all groupings

 - added link to download
 - added action download_groupings_files in SubmissionsController
bug fixed
added functional test
Merge master
Merge pull request #1132 from GhiGt/issue-969

Closes #969: remove fake path in message
Merge pull request #1134 from GhiGt/issue-1111

Closes #1111: possibility to download all submissions from all groupings