FLOE-171: Upgraded metadata demo with the new infusion model relay system

@amb26, can you review this pull request, our first pilot of the new model relay.
This change is introduced by https://github.com/fluid-project/infusion/pull/497 to fix this issue, http://issues.fluidproject.org/browse/FLUID-4698

I believe this code is to find the correct "html" container when both iframe and the main page are present. 

@jobara, feel free to correct me or add.