A button that launches a file chooser dialog.
The GtkFileChooserButton is very similar in
functionality to a GtkColorButton. It is a
special kind of button that allows the user to select a file.
The button contains an area that displays the file name of the current
file selected and also displays a button that allows the user to launch
a file selection dialog. After the dialog is launched, the button is
immediately associated to the new file selected by the user.