absolute pointer to the "mother" site in embed scripts should be injected

One of the steps of the deployment process involves a manual replacement of some of the HTML and JavaScript code used in the embedding code that we delivered to TeachHub. This replacement is necessary because the documents are copied elsewhere and they need to refer back to the "mother site", thus the deployment needs to change from current.dev.curriki.org, to beta.curriki.org, and www.curriki.org.

This site should be injected by a processing of the form of maven filtering.