Properly support custom namespaces

[mkrutov]

No description provided.

[mkrutov]

Currently, namespace generation is pretty much hardcoded into framework with no way around it. Need to support using custom namespaces instead of generated ones. Also need to look into how to properly pass namespaces to Builders since I'd prefer to pass Finalize()'d builders from tests to Framework.

[fgiorgetti]

One thing with finalized builders is. If you want to use a unique builder instance it is ok as long as you use only one namespace, or if you need to use multiple contexts, you'll need same namespace names across all of them, otherwise the namespace must be "modified" before calling the Build() method.