Add initial version of backup utility.

For now it supports interactive backup/restore from command line
and deamon mode which spawns Unix domain socket server for
controlling backup process.
Add paramiko library to use SFTP from Python.
Add support for controlling backup deamon using notifier.
Add model class representing pending and finished backup.
Improve Progress component.

* Add onFinished event
* Create dedicated mode for representing pending backup progress.
Initial version of web backup interface.
Gracefully respond to ^C.
Add backup/restore options to netcli.
Enlarge FlashDevice to 4GiB to fit the build.