hgweb: add a `web.view` to control filtering This options add a new `web.view` to control filter level of hgweb. This option have two purposes: 1) Allow fall back to unfiltered version in case a yet undetected by critical bug is found in filtering after 2.5 release 2) People use hgweb as a local repoviewer. When they have secret changesets, they wants to use "visible" filter not "served" (modified by mpm, documentation deferred)