These handle only VE-like products (think TWRP on Nexus 7);
the proper image support should be backported later on.

An experiment in layered configurations is still in its
early stages regarding ARM zoo...

This further refines the modular build by making
metadata being a clearly separated feature rather
than having to rely on runtime tests, and also by
moving the code which cares for kernel bits of base
installation (.base list) in a feature of its own.

There's more to it but let's get the ball rolling first.