improved dark mode, automatic theme switch (#5720)

assets/js/forms/KimaiFormSelect.js

@@ -80,6 +80,7 @@ export default class KimaiFormSelect extends KimaiFormTomselectPlugin {
             // if there are more than X entries, the other ones are hidden and can only be found
             // by typing some characters to trigger the internal option search
             // see App\Form\Type\TagsType::MAX_AMOUNT_SELECT
+            // TODO make this value configurable with a data attribute
             maxOptions: 500,
             sortField:[{field: '$order'}, {field: '$score'}],
             // required so it works in table.responsive, but requires z-index 1056, because bootstrap modal would otherwise hide it