[property editing] editing `application.yml` based property files doesn't work as good as `application.properties` files

[martinlippert]

I observed a few things that doesn't work the way they should:

server:
  port: 8080
  <*>

shows all kinds of properties, not just the one that are valid at the server level.
If selecting one of those random proposals, it is not inserted at the right level, but ends up looking like this:

server:
  port: 8088
	spring:
  activemq:
    broker-url:   

Also note that spring is intended with a tab instead of spaces (as the other lines are).

The other non-optimal part is the sorting of proposals, which seems to be a similar issue that we faced with #1342.