Improve update tool

[szszszsz]

Improve update tool so that it would :

• detect if device is in bootloader stage and continue if possible;
• suggest best solution for the given error (specifically lack of connection on regnual start);
• inform user about required packages to be installed (pyusb, cffi);
• do not allow to use CTRL+C without confirmation;
• remove usage of infinite loops while waiting;
• print the current version of the tool;
• release it to pip repository for easy access, without Git usage;
• add proper documentation.

Additional:

• make it standalone without pip (no Git usage needed);
• firmware download and verification (sha);
• firmware download and verification (sha + signature);
• simplify guide ;
• default to single LED color (red; with CLI fallback perhaps; do not offer text UI fallback right now);
• stop services from using the smart card during the update;
• ask for factory reset; ideally do it in script if will not take much time;
• add warning and to guide: close email clients and other smart card using applications;
• warn user to do not do anything during the update or the device will;
  be bricked;
• note to users: power cycle device at the end, on the success (?);
• remove debug verbosity (switch).

Details: https://support.nitrokey.com/t/nitrokey-start-benotigte-linux-pakete-fur-fimwareupdate/2228/9
Connected: #24

[szszszsz]

See https://github.com/Nitrokey/pynitrokey