Add ClearanceBackDoor for faster integration tests

https://trello.com/c/35ZtNHTi
Admin creates categories for account

* Rename feature files for consistency. Use noun-verb combination in
  present tense.
* Extract `/account_admin`
* Use normalize-rails for admin and account admin style.
* Add missing test coverage on User#account.
* Reduce routing interface.
* Add admin categories routes.
* Display accounts on admin dashboard.
* Display categories alphabetically.
* Find category links in admin feature spec.
* Use "Experience" objects, which are the same things as Page objects:
  http://code.google.com/p/selenium/wiki/PageObjects

https://trello.com/c/k4aCSs7O
Improve name of before_filter
Use more conventional root route
Use feature spec convention discussed in person

* Remove 'admin views dashboard' spec that is tested implicitly by
  other, more useful specs.
* Alias RSpec DSL.