Automatic twinterpreter invocation

[maxfischer2781]

While functions currently need an active handle to a twinterpreter, classes do not. Invoking a class lacking its twinterpreter could launch it automatically.

Ideally, twin masters should be singletons to avoid errors when trying to get a handle for function calls, after an implicit invocation via class.

[maxfischer2781]

Twin Masters and their helpers are already singletons, which check for consistency when trying to recreate them.