Add a route policy type "static-online" for files in public/ that
shouldn't be cached offline.
Put "static-online" files in the manifest NETWORK section instead of
in the CACHE section.
This code depends on PR 680. In addition, the docs include a link to
the proposed AppCache wiki page.
Adds the appcache smart package and associated documentation.
QA notes are in packages/appcache/QA.md (Is this a good place to put
them?)