Add a favicon option to cgitrc

This option is used to specify a shortcut icon on all cgit pages.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
diff --git a/ui-shared.c b/ui-shared.c
index 8a00099..6f83d2a 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -437,6 +437,11 @@
 	html("<link rel='stylesheet' type='text/css' href='");
 	html_attr(ctx->cfg.css);
 	html("'/>\n");
+	if (ctx->cfg.favicon) {
+		html("<link rel='shortcut icon' href='");
+		html_attr(ctx->cfg.favicon);
+		html("'/>\n");
+	}
 	html("</head>\n");
 	html("<body>\n");
 }