[panelset] output as default view

[Enchufa2]

Is it possible to set the default panel view? Or the panel ordering? It would be nice to be able to have an additional chunk option to e.g. invert code and output, so that the output is shown by default.

[gadenbuie]

After #193, you can now re-order the code and output panels

```{r panelset = c(output = "Plot", source = "ggplot2")}
ggplot(Orange) +
  aes(x = age, y = circumference, colour = Tree) +
  geom_point() +
  geom_line() +
  guides(colour = FALSE) +
  theme_bw()
```

or in Quarto syntax

```{r}
#| panelset:
#|   - output: Plot
#|   - source: ggplot2
ggplot(Orange) +
  aes(x = age, y = circumference, colour = Tree) +
  geom_point() +
  geom_line() +
  guides(colour = FALSE) +
  theme_bw()
```