WICKET-5674 Use jquery.atmosphere.js as a Webjar

(cherry picked from commit cd5d8f2b9084f923457b986a45c870620b1320e3)
WICKET-5674 Use jquery.atmosphere.js as a Webjar

Use IInitializer to setup webjars and not bother the developer to do it manually

(cherry picked from commit 9c74784080e9fad55b9a533cefa48b9ec9dca53c)
WICKET-5674 Use jquery.atmosphere.js as a Webjar

(cherry picked from commit d7775b1d2d38053dcadbbc9466d3f141b3072d06)
WICKET-5674 Use jquery.atmosphere.js as a Webjar

Use Sonatype snapshots repo for a version of Webjars that is built against Wicket 7.x