Review deploy-nuxeo.com-staging job

The job is now quite old and the pipeline usage has evolved; some limitations have been removed; good practices are being defined; etc.

Review https://qa.nuxeo.org/jenkins/job/Private/job/nuxeo.com-jobs/job/deploy-nuxeo.com-staging/ and all jobs matched by https://github.com/search?q=org%3Anuxeo+privovh02-2&type=Code

• allow redirects to be applied (independent of www.nuxeo.com)
• move pipeline to SCM
• use extended email (now available) and notify more than a unique person (requestor, culprits...)
• more generally, match the common Nuxeo usage on those "post build" actions
• improve branch naming convention (staging namespace rather than prefix)
• add/remove TODO in the source code

This is a follow up of https://jira.nuxeo.com/browse/NXBT-1367