FGFS-Addon: rewrite technical structure to namespace

[hbeni]

Currently the addon code lies mostly in the main function of addon-main.nas.
This has some side effects, one of them that the modules functions a not easily reachable from other code places.

It would be good to make a global namespace which then can be used from "anywhere", and the addons main() should just call whatever is needed into the global namespace.
This would also make loading/unloading easier.

One notable thing is that the calls to _setlistener() can be converted to the (future proof) setlistener().

[hbeni]

So, basicly already startet that by 8e76e23.

The global hash FGComMumble is made available in the submodules too, so basicly one can start to move functions and variables into that.
The submodules already use it to do logging, so that may serve as example on how to access it (its global and passed by reference).

From outside the module it ca be accessed by queriying the namespace from the addons module:
var fgcom_module = addons._modules["org.hallinger.flightgear.FGCom-mumble"].getNamespace()["FGComMumble"];

[hbeni]

Possibly obsoleted by FGCom-mumble integration into FGFS: https://gitlab.com/flightgear/flightgear/-/issues/3095