Use Forms API to load draft or at least provide "loading draft" feedback

Again, great and functional module, although it needs some user interface polishing.

When we open a draft for editing, we have to wait a few seconds until the draft is loaded. We have no feedback at all, so that someone in a hurry might think it's just broken.

There are two options for correcting it.

The first one is to load the content in the field in the Forms API (at PHP level). It'll load data from database and fill in Form API's[#default_value]s. It has the advantage of making the module a little more degradable. Of course we cannot save data without JS, but with this approach we could at least read saved draft data without JS.

Ok , it might perhaps be a little complicate to translate data saved with jQuery to Form API data. In this case, the second option is simple: just provide a loading feedback similar to the one described in #367171: Better presentation for "saving draft" feedback. Even better, we could also lock/hide all form fields while the draft is not loaded.

Again, I should be providing a patch in this issue, not just dropping off ideas. I'll be writing a patch and posting it here, very soon. For now, I'm just opening the discussion. What approach do you think is better?