Rename `formUrlPrefix` var to `URL_PREFIX`

* refs #18274
Change brand link to overview page

* Since there is no `home` in the proper sense, use the overview page as
  `home`.

* refs #18274
Change mail address in person's overview to a link

* This allows to write fast a mail to this person.

* refs #18358
Adjust column order in applications for leave list

* Column order should be consistent in list if possible.
  Adjust column order in list of applications for leave
  to the same order as on sicknotes page and staff page.

* refs #18603
Quick fix for overview calendar bug

* Holidays are not displayed in calendar in turn of the year case.
  Fetch not only holidays for the current year but for the next
  year too.

* NOTE: This quick fix is not nice at all, but only a quick solution.

* refs #17963
Release version 2.2.0
Prepare for next development iteration