Fixes COMETD-422 (websockets from https page).

Updated the Jetty Maven Plugin for the CometD demo to also run a SSL
connector.
The examples were mangling incorrectly the location by matching a
regexp that had "http" hardcoded; now "https?" is used.

Fixed also usage of Dojo from CDN, now referencing CometD locally
since it is not bundled in Dojo anymore, and using protocol relative
URLs such as "//some.cdn.com/path".