Closes #1078 : Be able to download all files submitted by a group

Addition of a method (get) 'downloads' to return a zip file of all
files in the repository.
 - Move from link to button.
 - Addition of translations.
 - Modification request from get to post.
Add button in result/edit page

- Add a conditional button in edit if there is files
- Add error checking in submission_controller.
Remove folders problems

 - Change directory's name of zipfile
Resolve buttons position issues

 - change type of method downloads in 'get'
 - (bonus) small indentation
Merging with master

 - Changing from result method to get_latest_result because it an array
now.
 - Deletion of return statements
 - Trying to respect the 80 chars
Merge remote-tracking branch 'origin/master' into issue-798
First changes for the tests
Mergin with origin/master
Adding a test for 'downloads' method in SubmissonConstroller
Add test when downloads is incorrect
respect 80 chars.
Fix: ruby 1.8 not set by default anymore
Merge pull request #1084 from GhiGt/issue-1078

Closes #1078 : Be able to download all files submitted by a group
Merge branch 'master' of github.com:benjaminvialle/Markus into update
Fix: array with ruby 1.9
Closes 997: Allow multiple files

 - Just adding of the attribute multiple
Closes #191: add unique index on DB level

 - adding of an index for annotation_categories
Merge pull request #1114 from GhiGt/issue-191

Closes #191: add unique index on DB level
Merge pull request #1101 from benjaminvialle/update

Fix: ruby 1.8 not set by default anymore