ListenTask cannot be called twice

[antho1404]

For now we cannot create our service calling listenTask multiple times and if we do we don't have any clear error message.

Solutions:

• Support multiple call
• Do not support multiple calls but have a better documentation about it and a error message to let the user know that multiple calls are not possible

[ilgooz]

I think we should still only support calling it once and throw an error in case of multiple calls. Because I cannot see any advantage of supporting multiple calls to listenTask since a service should implement all the defined tasks and start accepting execution request for them all the time.

But we're already throwing an error in case of multiple calls. @antho1404 Is this issue about mentioning this behaviour in the docs page?

[antho1404]

Yes we could improve the documentation and maybe having a better error in the code, it's quite confusing right now but maybe this PR https://github.com/mesg-foundation/mesg-js/pull/82 will solve that confusion

[NicolasMahe]

fixed