Support for sub-plugins, probably in V2

[Blue-Beaker]

Is your feature request related to a problem? Please describe.
I want to use custom IOs like GPIOs on my OrangePi Zero, USB relays, and custom sensors without the need to modify the plugin itself or create a fork.

Describe the solution you'd like
Implement support for sub-plugins, and split existing IO support to sub-plugins, like the PSU-Control Plugin does. So we users can create sub-plugins for this to support custom IOs without modifing the plugin itself.

Describe alternatives you've considered
Keep the existing IO support but mark the RPi dependencies optional (disable RPi-based functions on other devices instead), and just use custom shell script support for custom IOs.

Additional context
This would be a change that can break a a lot of things, so I suggest to implement this in the V2.