Can't override Prefixes from Cloned Sub-Items

Starting 5.1.0 we have introduced new was of parsing and caching classed for defined Unit Config.

This change affected the ability to override Sub-Item Prefixes created by Cloning from the general Prefix. One of the examples is Catalog Item Images (prefix: img), Comments (formal reviews, prefix: rev), Files (prefix: file) and some others.

In order to have this working we'll need to make some minor changes in Unit Config Reader, then create and start calling a special Event from where we can extend these needed classes