Feature Info plugins are run whenever the default feature-info box gets displayed (usually when the user clicks on a feature,
unless this behaviour has been over-ridden). They are able to add extra rows to the feature-info box. A minimal example is:
You can add either strings (as above) or DOM elements. If you want to add information which isn't yet available (e.g.
because you need to perform an AJAX request or other asynchronous operation to get hold of it), the simplest thing to
do is to add an empty div element then populate it once the data arrives