Remove modernizr (was only used for native datepicker detection)

Upgrade jQuery (1.10) and Handlebars (1.0)
Remove DatabaseCleaner in favor of single-threaded transaction specs

Use warden's login_as in feature specs instead of always logging in via
the form.

This shaves about ~25 seconds off the total test run speed
 * 20 from transactional fixtures
 * 5 from login_as