Alternative behaviour for DimmerService On/Off switch
At the moment, whenever you switch on a dimmer using HomeKit, it will set the brightness to 100%, as defined here:

https://github.com/thkl/homebridge-homematic/blob/c6dbf386e78b0fb90c6ce560a8c8835758c142c3/ChannelServices/HomeMaticHomeKitDimmerService.js#L40-L43

However, I would very much prefer the behaviour that turning the light on would set it to the _last brightness_ value. 

**Current behaviour:** 
Lamp On, 50 % brightness -> Lamp Off (will set it to 0% brightness) -> Lamp On (will set it to 100% brightness)
**Proposed behaviour:** 
Lamp On, 50 % brightness -> Lamp Off (will set it to 0% brightness) -> Lamp On (will set it to 50% brightness again)

Is there anything holding us back from implementing this (probably in a backwards-compatible manner)?