[core] Automatic saving of draft documents

Automatic save of documents as a 'draft',think like Gmail.

Could be at the backend (ideally) or browser level.

"1) I can't tell you how many times I've clicked away from an unsaved Workflow and lost all my work! are there plans for an autosave feature, or something similar? That would be great. If not that, at very least I'd like to get a warning from the browser when I try to leave a page on which there's unsaved work. (I've seen many web apps do this: when you try to leave a page you get a popup warning that if you leave, you'll lose unsaved work.)"