Preserve previous layout when upgrading firmware

[ahtn]

When new firmware is loaded, it also erases the layout and settings previously loaded on the device.

It should be possible to make them persist after an upgrade except for the encryption key which can't be retrieved. The steps to do this:

• Before the firmware update, download the layout and settings from the device (see keyplus-cli read --dump-layout --dump-settings).
• Remember the serial number of the device.
• Program the new firmware.
• Wait for the same device to connect again by looking for it's serial number
• Reprogram the settings that were downloaded before the update.