Fix DumpCommand to generate html with/out sandbox

api:doc:dump --format=html always disables the Sandbox since the check in
DumpCommand seems to be wrong. Fixed that as well as introduce a dummy
Request Object as the layout.html.twig expects an app.request object.
Merge pull request #290 from rajasaur/dumpcommand_bugfix

Fix DumpCommand to generate html with/out sandbox