Implements a basic PTT key via BLE HID using the optical pulse sensor as input device.
Just hover your hand over the sensor and the card10 will press the configured key. There is a menu to select which key to use and also which report to use.
Currently the keyboard and the consumer control reports are supported. The list of allowed keys is hard coded in the app. A later iteration might use introspection of the to get a list from the Adafruit library.