Beacon support

[Baggypants]

Related to the privacy request for randomised mac addresses. #736

I'd like to Beacon support to be considered and added to Infinitime. For my own use case I track bluetooth and Beacon devices around my house to trigger automations in homeassistant. The Infinitime firmware can be tracked using this existing method, but only when the watch isn't connected to a companion app. And I like my watch notifications too much to change that. Furthermore, if randomised mac address support is added (and it should be) I wouldn't be able to do that without knowing the private key of the device.

An example of Beacon support is built into the home assistant companion app. It sets up a 16 bit uuid that can be discovered by devices. I imagine that the broadcasting of a Beacon signal would have some impact on battery life.