Add support for drafts

[cheesemaker]

No description provided.

[manton]

We might want to punt drafts until version 3.1. One problem with saving drafts on the server is Sunlit would need to do something reasonable for drafts that were created in other apps. Or, we could support saving drafts but not editing drafts that were created outside Sunlit. Either could be a little confusing.

[cheesemaker]

Yes, this ticket is for future development, not 3.0.

[manton]

As I use the latest builds more, I'm thinking the first step is even simpler: just save the latest draft locally on the iOS device. This would avoid some of the issues with managing server drafts and still be really useful for what someone needs as they're composing a new post, going back and forth and adding multiple photos, etc.

[cheesemaker]

I think this is still too unknown. I'm moving this much further down the development path.