SupyML: Added correct handling of <success> messages and errors

[CorvusCorax]

in onceif/while statements, also added text quoting helper for compound responses.

I has these small improvements in the work, when I noticed that the original pull request was already merged.

While this improvement is not strictly needed, it makes use of SupyML easier (espcially regarding quoted multi-word responses) and more predictable when it comes to how error and success messages are interpreted by if/while statements

a success message is evaluated as "true" - regardless of the configured wording of that message - even if none a raised and uncaught error within the onceif/while expression is always considered false - regardless of the returned text

a success message along with a simultaneously propagating error message is considered False (example: eval truenope -- result: "Error: true")

[CorvusCorax]

@progval poke ;) did you see this?

[progval]

oops, I missed it