[refactor] Moved 'clearSelector' to its own TS file.

utils/uiHelpers/clearSelector.ts

@@ -0,0 +1,9 @@
+/**
+ * Clears all <option> elements from a <select>.
+ * @param selector The <select> element
+ */
+export function clearSelector(selector: HTMLSelectElement) {
+    for (let i: number = selector.options.length - 1; i >= 0; i--) {
+        selector.remove(i);
+    }
+}