Dungeon overview hides non-notable levels by default

Also, `#overview` no longer quits after viewing a single level.

These changes make the menu less awkward to use, and hiding non-notable
levels mirrors the behavior of the standard Dungeon Overview patch.

Against the coding standard, this undercuts the initial tab indent with
a 4-space indent to avoid having to either destroy blame history by
indenting the entire `dooverview()` function, or resorting to using a
goto in lieu of a loop.
Remove "store" from "a delicatessen store" in overview
Make YOU ARE HERE more obvious in dungeon overview

The level names and notes were making it hard to spot.  The original
Dungeon Overview patch formats the current level in bold, which DynaHack
doesn't have the ability to do.