[spec/feature] use correct table id
Merge pull request #317 from Genshin/fix_course_create_spec

[spec/feature] use correct table id
[view] attachments view
[concern] refacotred polymorhic controller
[routes] attachments routes
[spec/features] attachments under exam portionsa
[controller] attachments controller
[controller] clean unnecessery code from exam controller
[controller] set attachable for exam portion
[controller] remove unecessery controller
satisfy houndci
Various enhancements for Gaku::User:

* Remove defunct Gaku::User#has_role?
* Refactor and fix logic for Gaku::User#role?
* Add specs for all scopes and methods #to_s, #role?
* Document Gaku::User#find_first_by_auth_conditions
Merge branch 'master' of github.com:Genshin/gaku into add-tests-for-users
Bump ruby-version to 2.1.2
Merge pull request #320 from Genshin/bump-ruby

Bump ruby-version to 2.1.2
Merge pull request #318 from Genshin/refactor_and_ajaxify_attachments

Refactor and ajaxify attachments
Merge pull request #319 from Genshin/add-tests-for-users

Various enhancements for Gaku::User:
Merge branch 'master' of github.com:Genshin/gaku into group_class_group