Closes #1105: Be able to download all files with annotations

 - addition of the action 'download_zip' in ResultController
 - modification of the style to do not add a 'return' in the form
 - addition of the button 'Download all files' linked with the
'annotation' checkbox
added tests
Merge pull request #1123 from GhiGt/issue-1105

Closes #1105: Be able to download all files with annotations