Allow resource substitution nuvola:// URI
Allow resource substitution nuvola:// URI

WebWorker NavigationRequest has allowed resource substitution that
could theretically be HTTP/HTTPS URI. Now it is possible to provide
nuvola:// URI, which is resolved relative to web app's data dir.

Signed-off-by: Jiří Janoušek <2a48236b6dcae98c8c0e90f4673742773ee17d91@gmail.com>

tiliado/nuvolaruntime,tiliado/nuvolaruntime,tiliado/nuvolaruntime,tiliado/nuvolaruntime