v2.3.0b6 - Custom controllers

This minor change does not contain breaking changes.

✏️ Features

• Support for custom controllers (#12)
• Adding new predefined function for media players: next_source, previous_source
• E1810MediaPlayerController execute next and previous source when arrows are held

🎮 New devices

• Support for Xiaomi Aqara Smart Cube (z2m) @crserran
• Support for Xiaomi single switches WXKG12LM and WXKG01LM (z2m)
• Support for IM6001-BTP01, a SmartThings button (z2m, deconz, zha) @sreknob

Special thanks to @htvekov for all the bug hunting and testing.