Remove some Ruby 1.8-specific dependencies.
Upgrade capybara from 1.1 series to 2.2 series.
Upgrade uglifier from 2.2 series to 2.3 series.
Update bundler to 1.5 series.
Update rake.
Update uglifier to 2.4 series.
Travis: Also test on Ruby 2.0.0.
Merge remote-tracking branch 'origin/master' into coop

Conflicts:
	Gemfile
	Gemfile.lock
	features/step_definitions/notification_steps.rb