grpc namespace and not supported by older compilers. Not sure
why I didn't catch this earlier.

Clean up anything that failed

It was awkward for the generated code to call an API that offered
both insecure_server and secure_server as well as insecure_stub and
secure_stub. With this change there is just a single server function
and a single stub function and security is decided based on arguments
passed.

This is part of a change to ease internal usage of GRPC.

Refactors early_adopter such that interface-specific code is located in
the framework module as a submodule `alpha`.

With this change the Python code generated by the Python code generator
uses the grpc.early_adopter package and not the grpc.framework.face
package.

Fixes module path finding in the Python code generator and the signatures
of generated servicer methods.