Product Type class loader

The loader needs to be able to load the Product Type classes from external (product) repo.
Provide a way to load local classes too.

"the factory loader and the factory
itself need to be able to deal with [different branches of the same product types], e.g. by attaching the sha1 of
the source commit to the class name. that means that product types
referenced by a particular product can only come from coin (global
namespace) or the own repo+ref (local namespace), which seems like a
reasonable limitation at first sight. should that prove insufficient, it
would be possible to expose the local namespaces through the dependency
chains."

• sha1 of the Source commit needs to be appended into the class name
• support loading product type classes from global and local name space