Fhem tx

FHEM module now supports:
* battery and version messages
* power switch status message
* power switch on/off/toggle/statusRequest
* adds web commands to power switch
* verify and stores aes key

TODO:
* rename SHC -> SHC_BASE, SHC_TEMP -> SHC_DEVICE
* implement dimmer
* have a closer look at SHC_BASE driver and remove unused stuff copied from JeeLink