Optional secure pairing with a passkey

[evergreen22]

Support passkey pairing when requested by the central.
Also, fixes a comment and a reorder warning introduced by a faulty conflict resolution.

[geekbozu]

Looks good,
Thanks for staying on top of this!

[lman0]

work properly .
moreover unlike before , the passkey is shown only if gadgetbridge request a bonding
(basically , the passkey was automatically shown once bluetooth was activated , now it show itself only when we add infinitme as bond from gadgetbridge by the add device button).

thanks @evergreen22

[Avamander]

This is intentional?

[evergreen22]

Closes #880

[JF002]

Thank you very much, @evergreen22! Bluetooth pairing now works exactly as expected:

• Gadgetbridge : when connecting to the PinetTime, Gadgetbridge asks if the user wants to pair with the device. If he chose to pair, the PIN code is displayed on the PinetTime and can be entered in Gadgetbridge. If the user does not want to pair, vanilla connection is established.
• On Linux (Manjaro, KDE plasma), Siglo and Amazfish work exactly like before : they connect and communicate with the watch. Sometimes, KDE asks me if I want to "authorize and trust" my PineTime. I don't know what it does, but it doesn't ask for the PIN code and siglo/amazfish cannot connect anymore.
• On Linux, I can manually pair using bluetoothctl (type the command pair xx:yy:zz:11:22:33 and enter the PIN code displayed on the PineTime). Once it's done, Siglo/Amazfish can connect to the PineTime again.
• ITD supports secure pairing out of the box, and it works!

Great job everyone!

If I had only 1 suggestion : add a visual indicator showing if the connectivity is secured or not (ble icon with another color? another icon? something else?).

[JF002]

Update : according to my observations, OTA is much more reliable on not bonded connections! Using my new phone, it's nearly impossible to start an OTA (it fails at 0% after a few seconds) when bonded. WIthout the bond, OTA works as expected (and a lot faster with my new phone : 12kbps).

For some reason, it still works (bonded or not) on my older phone (but it's so slow... 2-3 kbps).

[evergreen22]

If I had only 1 suggestion : add a visual indicator showing if the connectivity is secured or not (ble icon with another color? another icon? something else?).

A padlock icon to the left of the ble icon would be nice when the connection is encrypted.