Add initial support for the keypad touch

[nickconway]

Initial support for the keypad touch. I currently have this working with home assistant on my own fork, and I can tell when a successful attempt was done. I'm sure there's more information to pull from it once there's official documentation.

Closes #250

[bdraco]

I’d probably add a note in the Home Assistant documentation that there is no encryption, so you shouldn’t rely on the sensor for secure operation