In case no distributed memory cache is specified this adds
a database backend for ratelimit purposes.
Signed-off-by: Lukas Reschke <lukas@statuscode.ch>
This introduces the defacto standard PSR-4 autoloader from composer into
core. This will allow proper PSR-4 naming of our classes.
Since our original autoloader is still available we can slowly switch
over classes to PSR-4.