Add define for own inclusion mode indication handler

[Maximilian Wache]

Feature request:
Add a feature for a custom indication handler for inclusion mode, similar to MY_INDICATION_HANDLER.

My use case:
Due to the limitation of the IO pin number on the ESP8266, I am using an I2C port extender.
This works well for MY_INDICATION_HANDLER, but I need a similar function for the inclusion mode display.