Updating demo

[jglick]

• using Updates workflow-aggregator-plugin#7
• picking up Change "-d" flag for "daemon" in wrapdocker to avoid deprecation jpetazzo/dind#103
• reworked snapshot builds in line with other demos
• figure out why Selenium tests still fail
• perhaps switch from DinD to bind-mounting the Docker socket as considered in Try to use --volumes-from instead of --volume ws:ws when Jenkins is containerized #31
• perhaps switch to multibranch
• perhaps run git daemon and EXPOSE 9418 like workflow-aggregator-plugin/demo/ does
• inherited directly from jenkinsci/jenkins rather than inheriting from jenkinsci/workflow-demo and then overriding/deleting much of it

@reviewbybees

[ghost]

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