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>

config/cfgroot/header.pl

@@ -91,7 +91,11 @@ if ( -d "/var/ipfire/langs/${language}/" ) {
     };
 };
 
+### Initialize user manual
+my %manualpages = ();
+&General::readhash("${General::swroot}/main/manualpages", \%manualpages);
 
+### Load selected language and theme functions
 require "${swroot}/langs/en.pl";
 require "${swroot}/langs/${language}.pl";
 eval `/bin/cat /srv/web/ipfire/html/themes/ipfire/include/functions.pl`;
@@ -553,3 +557,19 @@ sub colorize {
 		return $string;
 	}
 }
+
+# Get user manual URL for the specified configuration page, returns empty if no entry is configured
+sub get_manualpage_url() {
+	my ($cgi_page) = @_;
+
+	# Ensure base url is configured
+	return unless($manualpages{'BASE_URL'});
+
+	# Return URL
+	if($cgi_page && defined($manualpages{$cgi_page})) {
+		return "$manualpages{'BASE_URL'}/$manualpages{$cgi_page}";
+	}
+
+	# No manual page configured, return nothing
+	return;
+}

config/cfgroot/manualpages

@@ -0,0 +1,7 @@
+# User manual base URL (without trailing slash)
+BASE_URL=https://wiki.ipfire.org
+
+# Assign manual page URL path to CGI file ([cgi basename]=[path/to/page])
+index=configuration/system/startpage
+pppsetup=configuration/system/dial
+qos=configuration/services/qos