Yet another method for resource overview bar

Because that's just what it needs. Right.
What I should have done was commit my changes before splitting out
everything to _init_stats_gui, but there's no going back now. So here's
a short summary of what happened while moving:

* mostly removed special handling of summary line in layout and code
* simplified `format_display` to the point where it is no longer
  needed at all: Just use python's `+` string formatting
* documented layout hack a bit better
* several small coding style fixes