Added timezone and default date range settings.

hooks/useTimezone.js

@@ -0,0 +1,17 @@
+import { useState, useCallback } from 'react';
+import { getTimezone } from 'lib/date';
+import { getItem, setItem } from 'lib/web';
+
+export default function useTimezone() {
+  const [timezone, setTimezone] = useState(getItem('umami.timezone') || getTimezone());
+
+  const saveTimezone = useCallback(
+    value => {
+      setItem('umami.timezone', value);
+      setTimezone(value);
+    },
+    [setTimezone],
+  );
+
+  return [timezone, saveTimezone];
+}