Installs database cleaner

- preparation for feature tests with capybara
see:
http://devblog.avdi.org/2012/08/31/configuring-database_cleaner-with-rails-rspec-capybara-and-selenium/

spec/support/database_cleaner.rb

@@ -0,0 +1,22 @@
+RSpec.configure do |config|
+
+  config.before(:suite) do
+    DatabaseCleaner.clean_with(:truncation)
+  end
+
+  config.before(:each) do
+    DatabaseCleaner.strategy = :transaction
+  end
+
+  config.before(:each, :js => true) do
+    DatabaseCleaner.strategy = :truncation
+  end
+
+  config.before(:each) do
+    DatabaseCleaner.start
+  end
+
+  config.after(:each) do
+    DatabaseCleaner.clean
+  end
+end