Fill entry editor with entry data

[a-bakos]

Pulling entry data into admin editor view works. However, storing data on entry re-save is failing.

E.g. Create new post, fill in post data, save post (so far so good) Find your new post, go into edit mode, but don't change anything, just hit re-save. We'll lose the title. If you do the same but do change/update the title as well, the data is stored.

[a-bakos]

I'm merging this PR now, as the initial objective has been achieved and it's also getting excessively large.