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
Closes 997: Allow multiple files

 - Just adding of the attribute multiple
Deleting of my warning
Closes #474: Move custom validations to lib

 - Application of the patch
Merge pull request #1119 from GhiGt/issue-474

Closes #474: move custom validations to lib

We put our custom validators in a library validation class and then use validates.
Merge pull request #1100 from GhiGt/issue-798

Closes #760 : TA cannot choose 'filter' attribute properly
Merge pull request #1113 from GhiGt/issue-997

Closes 997: Allow student to send multiple files.
Closes #191: Remove index in annotation_categories

- Remove of last migration
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
addition of a message
Closes #265: Adding possibility to map grader to section

 - addition of a select in graders/index
 - modification of the filters tables, addition of a rule
Fix bug UI in browse

In reference with (PR) #1116 wich leave a bug in the display.
Closes #1124: Problems with importations

 - modification of the mistake
added tests
Closes #197: Encoding breaks

In reference with #197.

- added a Iconv encoding to allow possibility unlock codeviewer.
Merge pull request #1121 from GhiGt/issue-191

Closes #191: Remove index in annotation_categories
Merge pull request #1129 from GhiGt/bug-ui

Fix bug UI in browse
Merge pull request #1123 from GhiGt/issue-1105

Closes #1105: Be able to download all files with annotations
Merge pull request #1130 from GhiGt/issue-1124

Closes #1124: Problems with importations