Cleanup spec/support folder and spec/spec_helper

Changes:
* Move spec/monkeypatch to spec/support
* Remove unused support/shared_examples
* Move support/api to support/api_helpers to match module name
* Move support/login to support/login_helpers to match module name
* Move API specs to requests/api (convention over configuration)
* Remove unused support/js_patch
* Simplify login_as helper
* Move DatabaseCleaner stuff to its own support file
* Remove unnecessary configuration and requires from spec_helper

spec/support/api_helpers.rb

@@ -0,0 +1,9 @@
+module ApiHelpers
+  def api_prefix
+    "/api/#{Gitlab::API::VERSION}"
+  end
+
+  def json_response
+    JSON.parse(response.body)
+  end
+end