Peter Schlömer wrote:
This is actually a standard option in the preferences ("Misc", "Auto-number headings") of each user. I haven't tested this, but if I believe the documentation [1] you have to add the following line to LocalSettings.php to make this the default:
$wgDefaultUserOptions['editsection'] = 1;
The setting should be $wgDefaultUserOptions['numberheadings'] = 0;