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.
Closes #570 : Assignment due date with sections

- Add error message to show which section(s) is in past
- Add method to know the sections' names
- Modification of past_due_date? which doesn't work in some cases
Remove folders problems

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

 - change type of method downloads in 'get'
 - (bonus) small indentation
Fix: typo (missing +)
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
Changing from result to results because of the has_many
Update README.rst and markus-contributors.txt with students from UCOSP Winter 2013
Merge pull request #1093 from danielstjules/ucosp-contributors

Update README.rst and markus-contributors.txt with students from UCOSP Winter 2013
Merge pull request #1092 from GhiGt/patch-result

Changing from result to results because of the has_many
Ruby style for app/controller/api
Correction of errors in functional tests

Problem were due to the use of `create()` instead of `make()` function.
Exactly, the `is_remark` attribute were missed for the model
TextAnnotation.
Merge pull request #1094 from GhiGt/errors-functional-tests

Correction of errors in functional tests.
Prefer the use of make instead of create.
Ruby style for app/controllers/
Ruby style for app/helpers
Ruby style for app/controllers (mistake corrections)
Ruby style for app/models
Ruby style for app/ (mistakes correction)