[Version] Store version number in the options table

Store version number in the options table so that its easier to update for the frontend rather than the config.php which we don't really want to touch

application/views/debug/main.php

@@ -11,7 +11,7 @@
                 <table width="100%">
                     <tr>
                         <td>Version</td>
-                        <td><?php echo $this->config->item('app_version')."\n"; ?></td>
+                        <td><?php echo $this->optionslib->get_option('version')."\n"; ?></td>
                     </tr>
                     <tr>
                         <td>Language</td>