- Introduced generateDateMonthYearSelectionBox() which is suitable for e.g.

- Introduced generateDateMonthYearSelectionBox() which is suitable for e.g.
  birthday input fields.
- Introduced doTemplateDisplayReferralIdContent() template helper to get rid
  of an unneccessary if() block and $content[foo] in template
- Content of template register_header.tpl has now been moved to
  inc/language/register_de.php and has marked as deprecated
- Added new template (unfinished) for ext-wernis registration provider

Signed-off-by: Roland Häder <roland@mxchange.org>