Suggested data model first draft

Using this pull request to collaborate on the model - we'll move it somewhere else when we've agreed on it.
That might be useful indeed. There may be lots of different parts of the browser state that is interesting to applications, e.g. navigator.offLine, standalone state, whether the page is in a frame, DPR, orientation, performance events, etc. This is going to be an ever-growing set.

Perhaps there should be a dedicated top-level property for this? i.e. for any key-value pairs of any bit of context that oErrors can gather.