Add new model: Comment

- generate model comment
- add associations between comment and idea, comment and user
Add comment to idea

- Post comment on idea show page
Add comment controller

- create comment
Add comments' output on idea's view
Merge branch 'feature/comment' into develop

* feature/comment:
  Add comments' output on idea's view
  Add comment controller
  Add comment to idea
  Add new model: Comment
Merge branch 'develop' of https://github.com/hutusi/ideaegg into develop

* 'develop' of https://github.com/hutusi/ideaegg:
  Add footer to layout
  Add style to the form of idea page
  Add style to ideas#show page
  Add style to ideas#index page
  Add custom variables for Bootstrap
  Add font awesome
  Remove rails_layout
  Remove unused assets

Conflicts:
	app/views/ideas/show.html.erb
Translate comments' erb to slim