Change RevealJS paths to default folder structure of project

Using reveal.js/ pathing to javascript and css resources
to following pattern of other backends and simplifying
dependencying cloning for ADocs using this backend.

Default cloned or submodule add of RevealJS results
in a /reveal.js/ folder. Changing the paths in the
backend `document` HAML ensures users do not have
to sort/reorder and copy+paste resources for immediate
functionality.