Hide palette, if datalist palette is absent/empty

If showPalette is not set, but showDatalistPalette is set, only display the palette, if suggestions are available (i.e. @list is a valid reference to a datalist with enabled, non-empty options).

This state might change over time, so applyOptions() is called whenever datalistPalette is updated.
Merge pull request #1 from Dodo-87/master

Hide palette, if datalist palette is absent/empty