Deserialization of untrusted data in MelisFront

MelisFront is the engine that displays website hosted on Melis Platform. It deals with showing pages, plugins, URL rewritting, search optimization and SEO, etc. Attackers can deserialize arbitrary data on affected versions of `melisplatform/melis-front`, and ultimately leads to the execution of arbitrary PHP code on the system. Conducting this attack does not require authentication. Users should immediately upgrade to `melisplatform/melis-front` >= 5.0.1. This issue was addressed by restricting allowed classes when deserializing user-controlled data.