New bootloader & recovery firmware

This release brings the new recovery firmware based on InfiniTime. This firmware is intended to be used in conjunction with the new version for the bootloader I've just released.

This new MCUBoot bootloader fixes a few bugs and add new features and a new UI. Among these new features is the recovery functionality which allows to load a recovery firmware from the external flash memory to recover the PineTime when the current firmware cannot boot anymore.
This recovery firmware is a slightly modified version of InfiniTime that only provides a basic UI and the OTA functionality. You'll be able to use this firmware to load a new firmware over-the-air using BLE connectivity.

Note that all version of InfiniTime from 0.7.1 are and will be compatible with the previous MCUBoot bootloader (the one that is loaded at factory since September 2020) and the new version. The update is not mandatory.

Other than the recovery firmware, this release does not bring any new features in InfiniTime.