Instead the client is now created on the rust side based on the config.
Devices that require the mqtt client will now instead need to be
constructor using a function. This function receives the mqtt client.
Due to changes made in mlua the new scheduler is much simpler. It also
had no real business being part of the device manager, so it has now been
moved to be part of the returned config.
Instead of having to call all the module registration functions in one
place it is possible for each module to register itself in a global registry.
During startup all the all the modules will be registered
automatically.
This does currently have one weakness, to need to ensure that the crate
is linked.
