Implement frequency hoping

[ahtn]

Currently the code only use a fixed RF channel for the nRF24 radio. To improve RF performance in noisy environments it would be benefical to implement some form of channel hoping. The implementation would have need to be compatible with the unifying protocol.

Frequency hoping benefits the mouse more than the keyboard, and it adds a certain amount of overhead that is not present when using a fixed channel approach. So, ideally we should support both approaches.