Blender Git Loki

Altering the rules for opening a blender area window for render output.

- if current visible area shows render result; use this
- else: search for largest non-Image area (so it won't use Texture or
Composite outputs)
- else if only 1 available window it uses that one.

Works for both new options (fullscreen too). Especiall fullscreen works
much better, since it uses an own designated Image Window by default.