Feature/fresh status

> Reusing old cached state leads to a lot of problems (bad dependency
> resolving if things have changed, problems with backwards compatibility
> when service classes change, ...).
> The `restore_current_state` function now provides the guarantee that the
> restored state will never be older than x seconds (x=10minutes
> currently).

> This behaviour can be toggled with the `must_be_fresh` kwarg.
> The `info` command requires this, for example - we may render the
> cached state even if it is too old, it's just a visual thing and does no
> mutation.
Good idea (and unifies both "what about" points in the original comment ;o)