TS: being more delicate in handling Non-Generator returned Generator-Exceptions

Being: StopIteration and GeneratorExit
This is to prevent hard-to-debug behaviour and for all intents and purposes
unwanted anyway.
TS: removed ancient idea leftovers.
TS: removed unused testing class
TS: fixed handleNonGeneratorGeneratorExceptions original-exception string.

Implemented tests for Observable:
    - OnceMessage traceback fixing;
    - Non-Generator, generator-exception handling in message-handling.
TS: removed comments.