Deploy app using URL to a blueprint

Changes the behaviour of the "Create App" YAML tab to allow the user to
present a URL that contains the actual blueprint. The URL is fetched and
the content is used as a YAML blueprint.
Merge pull request #1436 from richardcloudsoft/deploy-using-url-to-blueprint

Deploy app using URL to a blueprint
Move RebindFailureMode enum into RebindManager i/f
Set rebind failure mode from brooklyn.properties