#51 + put chunks in separate steps; support rollback of putting chunks

Signed-off-by: Nico Rutishauser <nr@hotmail.ch>
Fix the update process: take existing protection keys

Signed-off-by: Nico Rutishauser <nr@hotmail.ch>
Optimize the update context

Signed-off-by: Nico Rutishauser <nr@hotmail.ch>
minor addition of log entry

Signed-off-by: Nico Rutishauser <nr@hotmail.ch>