Steps to reconnect to a presentation assume there's already a PresentationConnection

[markafoltz]

The steps to reconnect to a presentation (6.3.3., step 8) talk about using an existing PresentationConnection object to construct a new PresentationConnection. But if the page already has one it's not clear why we would need to construct a new one. It would be clearer to refer instead to the set of controlled presentations when constructing a new PresentationConnection.

[markafoltz]

On closer reading it's not a problem with the steps, it's just hard to keep track of the different objects. Tried to improve this with the PR.