webinterface: Add links to the configuration wiki

webinterface: Add links to the configuration wiki

This patch adds a little "help" icon to the page header.
If a manual entry exists for a configuration page, the icon
appears and offers a quick way to access the wiki.
Wiki pages can be configured in the "manualpages" file.

Signed-off-by: Leo-Andres Hofmann <hofmann@leo-andres.de>
Reviewed-by: Bernhard Bitsch <bbitsch@ipfire.org>
Tested-by: Bernhard Bitsch <bbitsch@ipfire.org>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>