Migration to rails 3.1

Done :
 - edited Gemfile
 - moved from public/ to assets/
 - added `config.assets.enable = true` in config/application.rb
 - commented lines about rjs in config/environments/development.rb
 - added lines about uglifier and scss
 - added app/assets/stylesheets/application.css
 - added app/assets/application.js

TODO:
 - move application.js in javascripts
 - resolve images not found
 - remove files not needed like rails.js, jquery.js...
update to rails 3.1.12
resolved sql problem
fix application.js

- moved application.js inside assets/javascripts
- removed jquery.js, prototype.js and rails.js to use the gems.
fix problem with ImageAnnotation
fix deprecation warnings
fix some errors

in
 - annotation_categories_controller_test.rb
 - assignments_controller_test.rb
fix flexible_criteria problems

added some fixtures files
fix some errors in notes_controller and grade_entry_forms_controller
fix some errors in tests

for:
 - results_controller_test
 - rubrics_controller_test
Merge branch 'master' into pr/1153
Merge branch 'master' into pr/1153
mysql2 >= 0.3 required in gemfile as of Rails 3.1
Fix exception type mismatch in create_or_update_from_csv_row in rubric_criterion.rb
Fixed functional test cases for move_criterion
Flash now requires has? rather than has_key?
Fixed issue 957: new submission rule links only appear after the radio button has been selected and after all submission rule partial forms. Also added that the rules not being used are hidden.
Fix for issue 1048: Fixed error message for unrelasing incomplete assignments
Mistakenly deleted % from penalty_decay_period partial in previous commit
Changed 'each' to 'every' in penalty decay submission rule partial form.