Added basic authentication and CRUD actions for users.

Includes addition of capybara gem configured for feature tests.
Note capybara has runtime dependency on nokogiri and might not work
on Windows. See https://github.com/sparklemotion/nokogiri/issues/864

Conflicts:
	app/models/user.rb
	app/views/layouts/application.html.erb
	config/routes.rb
	spec/models/user_spec.rb
	spec/spec_helper.rb
Merge authentication branch.