WIP: Modifying iframe_sample_app to send and receive messages

:construction: Earlier the iframe_sample_app used to display content from an external website (Wikipedia).

/cc @zendesk/quokka 

### References
- Issue #59

### Risks
 - None
I will be adding in the readme that you need to have the zaf sdk running locally. That is going to be open source so people can see in the code what is being sent in ```data```. Do you think this ```data.awesome``` bit will be clear then?