Allow BLE connection to more than one device

[riban-bw]

Currently InfiniTime (on PineTime) will only connect to a single device at a time, e.g. mobile phone. This suits most users who want their watch paired with their phone but there are some use cases where multiple connections would be advantageous.

Aome users wish to sync their phone and their computer to the watch for notifications from various apps. I am working on an (niche) application for interfacing the watch with synthesisers (specifically Zynthian) via BLE MIDI. I want the watch to continue to be connected to my phone whilst I also connect to the Zynthian for musical interaction.

NimBLE supports multiple connections (32+) so this should be possible. Of course there would be some overhead for managing the connections so it might want to be a configurable option, maybe enabled at compile time.