Transitions between pages needs to be refined (invent channels for lifecycle events)

[ntoll]

Currently, transitions between pages are a quick bodge. We need a way for the coder to signal to the Invent framework that the current page should be replaced by a new page. What actually happens is that all pages always exist in the DOM, but they're all hidden except for the current page.

We discussed the possibility of having default Invent channels for app lifecycle events - where the coder can trigger something app related, or the app can signal something app related has happened. Perhaps there should simply be a default channel called app to which only a small set of messages can be published?