The term "cancelling" is used with GCancellable, a user clicking a close
button is not that.
User input is usually described as "dismissing", so we use that term.
These are being replaced by GtkColorDialog
and GtkColorDialogButton.
This commit only moves the headers for GtkColorChooserWidget
and GtkColorChooserDialog to deprecated/, and keeps the
implementations in gtk/, since they will eventually be
salvaged into a private GtkColorChooserWindow.