Add Python API to update the firmware and the SSL security files (certificates and keys).

[danicampora]

Also improve the software update mechanism to have 2 user update files, this way, if a software update fails, the current firmware still remains active instead of falling back to the factory version. Improve the safe boot process so that it allows to go back to an older user update or to the factory firmware. This ticket MUST be solved before shipping the WiPy's in August since it involves changing the bootloader.

[danicampora]

The mechanism with 2 user update files is implemented here:
micropython@e955089

The Python API to access the file updater will come on a later patch.

[danicampora]

I have been thinking that no special API is needed. Updating of this files will be simply done like the way it's done by the FTP server (just like any other file but on the special paths /flash/sys and /flash/cert).

[dpgeorge]

Updating of this files will be simply done like the way it's done by the FTP server

Sounds good.

[danicampora]

@dpgeorge cool, thanks for taking a look a this :-).