Make cloud integration the default experience

Notes has some cloud support but it's not generally treated as the primary or default experience. If we really want to get people using Notes, this has to change: backup, sync and mobile support have to become a core part of the experience.

To do this, we need to pick a primary service/protocol to use for cloud sync, and make that the default experience.

Ideally, whatever service/protocol we pick should have a mobile app already available. We also need to think about the featureset of the service and how this might impact the Notes user experience.

It would be great if we could use this issue to evaluate the options.