Cleanup: no need for assignment to '_return'

The last line of the clause is an implicit return; it's idiomatic
to just leave it bare.
Dynamically load translator modules by name

The infrastructure is now in place that will translate the
name of a client type as written in the server config file
to an actual translator module that can be loaded and used
in client process code.
Dynamically spawn supervised client processes

We've just wired up the last of the code we need to handle
arbitrary numbers of clients connected to the server
simultaneously.