Update Jbuilder.
Add examples to pending helper and view tests.
Remove request specs and add feature specs.

Headless, Database Cleaner, and a WebKit JavaScript driver for Capybara
have been added so feature specs can be handled properly. Transactional
examples and fixtures don't work too well with feature specs, so
Database Cleaner takes over with those specs. The WebKit JavaScript
driver handles examples that need it without the need of opening a web
browser (e.g., Firefox). The Headless gem manages Xvfb. Xvfb is needed
by the JavaScript driver on headless Linux systems and on Travis CI.