Switch to `vendor-mmlc` directory

[grandeljay]

After updating to modified 3.1.0, my logs are being flooded with:

Using file vendor-no-composer/autoload.php is deprecated. Use vendor-mmlc/autoload.php instead.

I vaguely remember this not being changed deliberately, due to a possible incompatibility with old MMLC versions or similar. Perhaps now is a better time to make the change?

[RobinTheHood]

Maybe we can implement a mechanism so that certain messages are only generated or written to the logs once per hour or once per day.