Added support for proprietary devices

[apachler]

This feature makes it possible to inject proprietary device information the way BACpypes3 handels it.

To inject devices it is needed to import a custom class, atm this is only possible for advanced users since it is needed to implement a custom AsyncBACnetConnector class.

This PR makes sure the actual BACnet connector implementation is able to handle it.

[apachler]

I am working on a clean way to inject proprietary devices classes without the need of defining custom AsyncBACnetConnect.
Since i am not sure how long this will take, it would be nice to have that PR merged so everyone can use the more advanced way.

[apachler]

Please do not merge this PR for now ...

[apachler]

Feature done with dynamic loading of custom device extension.

In folder extensions/bacnet/proprietary there is a sample file how custom objects have to be defined. All files in this directory are imported dynamically on connector start.

[apachler]

@imbeacon any comments?

[samson0v]

@apachler, thanks for the PR. I will review it soon.

[samson0v]

@apachler, also, please, revert changes for the uplink converter, as it was fixed.
We are planning a release tomorrow. Could you resolve the points above, so your feature will be included?

[apachler]

@apachler, also, please, revert changes for the uplink converter, as it was fixed. We are planning a release tomorrow. Could you resolve the points above, so your feature will be included?

done, hopefully i did it to your liking ;)

[samson0v]

@apachler, well done! Thanks for your contribution!
I will merge your PR today.