Wishlist: auto.key should allow default components to be suppressed

Maybe this should be easier:

```r
barchart(VADeaths, border = "transparent",
         par.settings = simpleTheme(pch = 16, col = 2:5),
         auto.key = list(points = TRUE, rectangles = FALSE))
```

Possibly just with

```r
           auto.key = list(points = TRUE, rect = FALSE))
```

