Make a better switcher between code and data.

[fdb]

The problem is that if data can only be represented as data (e.g. CSV), the default view is the ugly last resort viewer. In this case, we want to switch to the data panel immediately and disable the viewer option.

But we can look at it differently. If we make the viewer / data into a menu, we can have many options. We can have multiple visualisers for color, for example. If there's only option available, like in the CSV case, we can choose it automatically and disable the menu.