Merge pull request #720 from Originate/dev

Dev
set up the `Comment` model
[style] comment partial, comment form and their stylesheet
Route for Comment
comment_controller and corresponding js views
[chore]remove .hide from box_content_modal to show it
[refactor] rename `box_content_modal` to `sign_in_modal`
[style] rename modal ids

- rename modals for different uses
[validation] content of the comment can't be blank
[authentication] user can only delete his/her own comments
[style] article has_many comments
[js] js way to check whether user has signed in
[test] FactoryGirl for `comment`
[test] set up integration test for comment
[chore]show guideline for posting content in expert dashboard
Merge pull request #646 from Originate/change_bs2.3_to_bs3

Change bs2.3 to bs3
[chore]show preview for posting article

Note: still to fix css to show it correctly
Merge pull request #722 from Originate/change_bs2.3_to_bs3

[chore]show preview for posting article
[chore]remove config/../remove-this... to avoid duplicate config
Merge pull request #723 from Originate/change_bs2.3_to_bs3

[chore]remove config/../remove-this... to avoid duplicate config