Use a mysql database for session handling

.gitmodules

@@ -15,3 +15,6 @@
 [submodule "lib/modulekit/ajax"]
 	path = lib/modulekit/ajax
 	url = https://github.com/plepe/modulekit-ajax.git
+[submodule "lib/modulekit/mysql-sessions"]
+	path = lib/modulekit/mysql-sessions
+	url = https://github.com/plepe/PHP-MySQL-Sessions.git

conf.php-dist

@@ -107,3 +107,9 @@ $languages = array(
   "sr", // Serbian
   "uk", // Ukrainian
 );
+
+// Uncomment the following lines to use a MYSQL database for session handling.
+// Create database table 'sessions' as described in
+// https://github.com/plepe/PHP-MySQL-Sessions/blob/master/README.md
+#include "lib/modulekit/mysql-sessions/mysql.sessions.php";
+#new Session(new PDO('mysql:dbname=DB', 'USER', 'PASSWORD'));

lib/modulekit/mysql-sessions

@@ -0,0 +1 @@
+Subproject commit 3aa1bc06badb51c351ac6d041052a603d0cdd554