Added missing 'rev' property to feature.

I've missed to store revisions of new documents somewhere. Since feature
collections are agnostic to any other fields except for 'properties' and
'geometry', this would be the place to go, I presume.
Moved rendering "#modify div" into build_modify().
Fixed uncaught error on submit->reduce->revert->submit.

"#div modify" needs to be refreshed to represent
feature.properties.GeoJSON_clone.
Minor optical changes.

That is, a new line for every function and I used 'show_fields' instead of
'build-whatever'. Now it's starting to look like a little less of retarded
scripting.