added a draft of a presscomposer example, in need of verification

I couldn't find any examples of pressComposers. I tried some stuff, and some of it worked fine in a browser but not when it got to a touch device. Would the event page be an okay place to add a press composer example? 

This draft has a few TODOs 

- [ ] verify if the removeEventListener is actually required, or if its the right ones, and why
- [ ] verify the actual method for hover, if any
- [ ] is there an easier way to declare a pressComposer in the serialization?