[FFe] Continue development of snappy features

[Sergio Schvezov]

I request this FFe since snappy is still in development, these features only apply to the ubuntu-device-flash componenet delivered in this package and to the 'core' subcommand.

The missing features include:
- snappy package install support.
- complete oem snappy package support.
- add store login support.

This package lives in universe, most consumers of this package (ci included) consume it from a PPA, so deprecation rules and non breaking new features are always taken into account.