Closes #1073: Possibility to import/export assignments

 - add upload and download link
 - add actions in AssignmentController
 - modification of required fields for an assignment

/!\ Some modification are still needed
added encoding with iconv
added some tests and fixed a bug
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
Merge branch 'master' into issue-1073
somes small changes
bug fixed
Merge branch 'master' into issue-1073
Closes #1136: Switching revision number

 - added a revisions_history attribute to repo_browser
 - added a select in repo_browser
fix i18n
Closes #1143: Remove all fixtures

 - removed all fixtures
 - removed all fixtures calls
 - Edited some tests to replace fixtures with blueprint
fix problem with fixtures/ directory

 - moved files called by fixture_file_upload in
test/fixtures{files/classlist-csvc}
Closes #1126: Missing fields in an Assignment

 - added validates to :description and assignment_stat
Removed a comment
Fix: tests with FlexibleCriterion
removed old form tag
removed other useless variables
added functional test
Merge master