Merge pull request #17 from udacity/development

Emergency fix - skip user profile sync if there is no active user
Merge pull request #19 from udacity/development

Merged with updates from upstream
Merge pull request #21 from udacity/development

Merged with updates from upstream
Merge pull request #23 from udacity/development

Merged development
adding activities migration and model
adding activities migration
Adding activities, tests, API, backend, and everything
增加移动版Header和样式表
Minor fixes

* add discourse to sudo
* add `bundle exec` on some calls
* inform user of NUM_WEB/sockets count for nginx config
Adding activities
Adding subcategories
Merge pull request #26 from udacity/development

Merged with updates from upstream
Refactor: Topic#invite_by_email

Extract Topic#email_already_existas_for? and Topic#grant_permission_to_user
Adding un-sub-categorized site setting.
Adding un-sub-categorized site setting.
Adding un-sub-categorized site setting.
No sudo perm for user

Also changed order on informing user that he'll be encountering errors that needs admin access before calling `rvm`.
Merge pull request #28 from udacity/development

Merge latest changes from upstream.
suggested BBS copy change for inappropriate flag
fix amazon onebox to pull images again